String

Introduction

String is probably the most commonly used class in Java’s class library. The obvious reason for this is that strings are a very important part of programming. The first thing to understand about strings is that every string you create is actually an object of type String. Even string constants are actually String objects.

For example, in the statement the string "This is a String, too" is a String object.

System.out.println("This is a String, too");

The second thing to understand about strings is that objects of type String are immutable; once a String object is created, its contents cannot be altered. While this may seem like a serious restriction, it is not, for two reasons:

• If you need to change a string, you can always create a new one that contains the modifications.

• Java defines peer classes of String, called StringBuffer and StringBuilder, which allow strings to be altered, so all of the normal string manipulations are still available in Java.

Strings can be constructed in a variety of ways. The easiest is to use a statement like this:

String myString = "this is a test";

Once you have created a String object, you can use it anywhere that a string is allowed.

For example, this statement displays myString:

System.out.println(myString);

Java defines one operator for String objects: +. It is used to concatenate two strings. For example, the following statement results in myString containing "I like Java."

String myString = "I" + " like " + "Java.";

The following program demonstrates the preceding concepts:

Example 15.1: Creating strings

// Demonstrating Strings.

class StringDemo {

public static void main(String args[]) {

String strOb1 = "First String";

String strOb2 = "Second String";

String strOb3 = strOb1 + " and " + strOb2;

System.out.println(strOb1);

System.out.println(strOb2);

System.out.println(strOb3);

}

Here are a few. You can test two strings for equality by using equals( ). You can obtain the length of a string by calling the length( ) method. You can obtain the character at a specified index within a string by calling charAt( ). The general forms of these three methods are shown here:

boolean equals(secondStr);

int length( );

char charAt(index);

Here is a program that demonstrates these methods.

Example 15.2: Manipulating strings

// Demonstrating some String methods.

class StringDemo2 {

public static void main(String args[]) {

String strOb1 = "First String";

String strOb2 = "Second String";

String strOb3 = strOb1;

System.out.println("Length of strOb1: " +

strOb1.length());

System.out.println("Char at index 3 in strOb1: " +

strOb1.charAt(3));

if(strOb1.equals(strOb2))

System.out.println("strOb1 == strOb2");

else

System.out.println("strOb1 != strOb2");

if(strOb1.equals(strOb3))

System.out.println("strOb1 == strOb3");

else

System.out.println("strOb1 != strOb3");

}

Of course, you can have arrays of strings, just like you can have arrays of any other type of object.

Example 15.3: Collection of strings

// Demonstrate String arrays.

class StringDemo3 {

public static void main(String args[]) {

String str[] = { "one", "two", "three" };

for(int i=0; i<str.length; i++)

System.out.println("str[" + i + "]: " +

str[i]);

}

Command line argument

Sometimes you will want to pass information into a program when you run it. This is accomplished by passing command-line arguments to main( ). A command-line argument is the information that directly follows the program’s name on the command line when it is executed. To access the command-line arguments inside a Java program is quite easy—they are stored as strings in a String array passed to the args parameter of main( ). The first command-line argument is stored at args[0], the second at args[1], and so on.

For example, the following program displays all of the command-line arguments that it is called with:

Example 15.4: Creating strings as arguments in Java’s main()

class CommandLine {

public static void main(String args[]) {

for(int i=0; i<args.length; i++)

System.out.println("args[" + i + "]: " + args[i]);

}

Constructors in class String

Constructor	Description
String()	Initializes a newly created String object so that it represents an empty character sequence.
String(byte[] bytes)	Constructs a new String by decoding the specified array of bytes using the platform's default charset.
String(byte[] bytes, Charset charset)	Constructs a new String by decoding the specified array of bytes using the specified charset.
String(byte[] ascii, int hibyte)	This method does not properly convert bytes into characters. As of JDK 1.1, the preferred way to do this is via the String constructors that take a Charset, charset name, or that use the platform's default charset.
String(byte[] bytes, int offset, int length)	Constructs a new String by decoding the specified subarray of bytes using the platform's default charset.
String(StringBuffer buffer)	Allocates a new string that contains the sequence of characters currently contained in the string buffer argument.
String(StringBuilder builder)	Allocates a new string that contains the sequence of characters currently contained in the string builder argument.
String(byte[] bytes, int offset, int length, Charset charset)	Constructs a new String by decoding the specified subarray of bytes using the specified charset.
String(byte[] ascii, int hibyte, int offset, int count)Deprecated.	This method does not properly convert bytes into characters. As of JDK 1.1, the preferred way to do this is via the String constructors that take a Charset, charset name, or that use the platform's default charset.

String(byte[] bytes, int offset, int length, String charsetName)	Constructs a new String by decoding the specified subarray of bytes using the specified charset.
String(byte[] bytes, String charsetName)	Constructs a new String by decoding the specified array of bytes using the specified charset.
String(char[] value)	Allocates a new String so that it represents the sequence of characters currently contained in the character array argument.
String(char[] value, int offset, int count)	Allocates a new String that contains characters from a subarray of the character array argument.
String(int[] codePoints, int offset, int count)	Allocates a new String that contains characters from a subarray of the Unicode code point array argument.
String(String original)	Initializes a newly created String object so that it represents the same sequence of characters as the argument; in other words, the newly created string is a copy of the argument string.

Methods in class String

Method	Description
contains(CharSequence s)	Returns true if and only if this string contains the specified sequence of char values.
contentEquals(CharSequence cs)	Compares this string to the specified CharSequence.
contentEquals(StringBuffer sb)	Compares this string to the specified StringBuffer.
copyValueOf(char[] data)	Returns a String that represents the character sequence in the array specified.
copyValueOf(char[] data, int offset, int count)	Returns a String that represents the character sequence in the array specified.
endsWith(String suffix)	Tests if this string ends with the specified suffix.
equals(Object anObject)	Compares this string to the specified object.
equalsIgnoreCase(String anotherString)	Compares this String to another String, ignoring case considerations.
format(Locale l, String format, Object... args)	Returns a formatted string using the specified locale, format string, and arguments.
format(String format, Object... args)	Returns a formatted string using the specified format string and arguments.
getBytes()	Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.
getBytes(Charset charset)	Encodes this String into a sequence of bytes using the given charset, storing the result into a new byte array.

getBytes(int srcBegin, int srcEnd, byte[] dst, int dstBegin)Deprecated.	This method does not properly convert characters into bytes. As of JDK 1.1, the preferred way to do this is via the getBytes () method, which uses the platform's default charset.
getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)	Copies characters from this string into the destination character array.
hashCode()	Returns a hash code for this string.
indexOf(int ch)	Returns the index within this string of the first occurrence of the specified character.
indexOf(int ch, int fromIndex)	Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.
indexOf(String str)	Returns the index within this string of the first occurrence of the specified substring.
indexOf(String str, int fromIndex)	Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
intern()	Returns a canonical representation for the string object.
isEmpty()	Returns true if, and only if, length() is 0.
lastIndexOf(int ch)	Returns the index within this string of the last occurrence of the specified character.
lastIndexOf(int ch, int fromIndex)	Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.
lastIndexOf(String str)	Returns the index within this string of the last occurrence of the specified substring.
lastIndexOf(String str, int fromIndex)	Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.
length()	Returns the length of this string.
matches(String regex)	Tells whether or not this string matches the given regular expression.
offsetByCodePoints(int index, int codePointOffset)	Returns the index within this String that is offset from the given index by codePointOffset code points.
regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)	Tests if two string regions are equal.
regionMatches(int toffset, String other, int ooffset, int len)	Tests if two string regions are equal.
replace(char oldChar, char newChar)	Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
replace(CharSequence target, CharSequence replacement)	Replaces each substring of this string that matches the literal target sequence with the specified literal replacement sequence.
replaceAll(String regex, String replacement)	Replaces each substring of this string that matches the given regular expression with the given replacement.
replaceFirst(String regex, String replacement)	Replaces the first substring of this string that matches the given regular expression with the given replacement.
split(String regex)	Splits this string around matches of the given regular expression.
split(String regex, int limit)	Splits this string around matches of the given regular expression.
startsWith(String prefix)	Tests if this string starts with the specified prefix.
startsWith(String prefix, int toffset)	Tests if the substring of this string beginning at the specified index starts with the specified prefix.
subSequence(int beginIndex, int endIndex)	Returns a new character sequence that is a subsequence of this sequence.
substring(int beginIndex)	Returns a new string that is a substring of this string.
substring(int beginIndex, int endIndex)	Returns a new string that is a substring of this string.
toCharArray()	Converts this string to a new character array.
toLowerCase()	Converts all of the characters in this String to lower case using the rules of the default locale.
toLowerCase(Locale locale)	Converts all of the characters in this String to lower case using the rules of the given Locale.
toString()	This object (which is already a string!) is itself returned.
toUpperCase()	Converts all of the characters in this String to upper case using the rules of the default locale.
toUpperCase(Locale locale)	Converts all of the characters in this String to upper case using the rules of the given Locale.
trim()	Returns a copy of the string, with leading and trailing whitespace omitted.

Example 15.5: Extracting substring of a string

The following program uses substring( ) to replace all instances of one substring with another within a string:

// Substring replacement.

class StringReplace {

public static void main(String args[]) {

String org = "This is a test. This is, too.";

String search = "is";

String sub = "was";

String result = "";

int i;

do { // replace all matching substrings

System.out.println(org);

i = org.indexOf(search);

if(i != -1) {

result = org.substring(0, i);

result = result + sub;

result = result + org.substring(i + search.length());

org = result;

}

} while(i != -1);

}

Example 15.6: Merging two strings

You can concatenate two strings using concat( ). This method creates a new object that contains the invoking string with the contents of str appended to the end. concat( ) performs the same function as +. For example,

// String concatenation (merging).

class StringMergingDemo {

public static void main(String args[]) {

String s1 = "Debasis";

String s2 = s1.concat("Samanta");

System.out.println(s1);

System.out.println();

System.out.println(s2);

// Alternatively, + performs the same, for example

String s1 = "Debasis";

String s2 = s1 + "Samanta";

System.out.println(s1);

System.out.println();

System.out.println(s2);

}

Example 15.7: Replace character(s) in a string by another character(s)

Thee is the replace( ) method which has two forms to this task. The first replaces all occurrences of one character in the invoking string with another character. The second replaces a sequence of characters with another sequence of characterts.

// Replacing characters in a string.

class StringReplaceDemo {

public static void main(String args[]) {

String s1 = "Java";

String s2 = s1.replace(‘a’, ‘u’); // Replace all occurrences of ‘a’ with ‘u’

System.out.println(s2);

System.out.println();

String s3 = "top and pop";

String s4 = s.replace(“op”, “oop”); // Replace “op” with “oop”

System.out.println(s4);

}

Example 15..8: Removing leading and railing whitespaces in a string

// Using trim() and equals() to process commands.

import java.io.*;

class StringTrimDemo {

public static void main(String args[]) throws IOException. {

// create a BufferedReader using System.in

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

String str;

System.out.println("Enter 'stop' to quit.");

System.out.println("Enter country: ");

do {

str = br.readLine();

str = str.trim(); // Remove whitespace

if(str.equals("India"))

System.out.println("Capital is New Delhi.");

else if(str.equals("America"))

System.out.println("Capital is New York");

else if(str.equals("England"))

System.out.println("Capital is London");

else if(str.equals("Singapore"))

System.out.println("Capital is Singapore!");

} while(!str.equals("stop

}

Example 15..9: Changing the case of characters within a string

// Demonstrate toUpperCase() and toLowerCase().

class ChangeCaseDemo {

public static void main(String args[]) {

String s = "This is a test.";

System.out.println("Original: " + s);

String upper = s.toUpperCase();

String lower = s.toLowerCase();

System.out.println("Uppercase: " + upper);

System.out.println("Lowercase: " + lower);

}

Example 15.10: Joining strings with delimiter

JDK 8 adds a new method to String called join( ). It is used to concatenate two or more strings, separating each string with a delimiter, such as a space or a comma. The following program demonstrates this version of join( ):

// Demonstrate the join() method defined by String.

class StringJoinDemo {

public static void main(String args[]) {

String result = String.join(" ", "Alpha", "Beta", "Gamma");

System.out.println(result);

result = String.join(", ", "Java", "query","E-mail: java@google.com");

System.out.println(result);

}

StringBuffer Class

The major limitation with String objects is that they are immutable, that is, once you create an object, it cannot be modified; for example, cannot insert, delete and append a character into it. On the other hand, an object of the class StringBuffer is like a String, but can be modified. At any point in time, a StringBuffer object contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls. Further, a StringBuffer object is thread-safe. The major difference between the two classes are summarized in the table given below.

String	StringBuffer
String class is immutable.	StringBuffer class is mutable.
String is slow and consumes more memory when you concat too many strings because every time it creates new instance.	StringBuffer is fast and consumes less memory when you cancat strings.
String class overrides the equals() method of Object class. So you can compare the contents of two strings by equals() method.	StringBuffer class doesn't override the equals() method of Object class.

Modifying a String

Because String objects are immutable, whenever you want to modify a String, you must either copy it into a StringBuffer or StringBuilder, or use a String method that constructs a new copy of the string with your modifications complete. A sampling of these methods are described here.

Class StringBuffer

StringBuffer supports a modifiable string. As you know, String represents fixed-length, immutable character sequences. In contrast, StringBuffer represents growable and writable character sequences. StringBuffer may have characters and substrings inserted in the middle or appended to the end. StringBuffer will automatically grow to make room for such additions and often has more characters preallocated than are actually needed, to allow room for growth.

StringBuffer constructors

StringBuffer defines these four constructors:

Constructor	Description
StringBuffer()	Constructs a string buffer with no characters in it and an initial capacity of 16 characters.
StringBuffer(CharSequence seq)	Constructs a string buffer that contains the same characters as the specified CharSequence.
StringBuffer(int capacity)	Constructs a string buffer with no characters in it and the specified initial capacity.
StringBuffer(String str)	Constructs a string buffer initialized to the contents of the specified string.

The default constructor (the one with no parameters) reserves room for 16 characters without reallocation. The second version accepts an integer argument that explicitly sets the size of the buffer. The third version accepts a String argument that sets the initial contents of the StringBuffer object and reserves room for 16 more characters without reallocation. StringBuffer allocates room for 16 additional characters when no specific buffer length is requested, because reallocation is a costly process in terms of time. Also, frequent reallocations can fragment memory. By allocating room for a few extra characters, StringBuffer reduces the number of reallocations that take place. The fourth constructor creates an object that contains the character sequence contained in chars and reserves room for 16 more characters.

StringBuffer methods

Method	Description
append(boolean b)	Appends the string representation of the boolean argument to the sequence.
append(char c)	Appends the string representation of the char argument to this sequence.
append(char[] str)	Appends the string representation of the char array argument to this sequence.
append(char[] str, int offset, int len)	Appends the string representation of a subarray of the char array argument to this sequence.
append(CharSequence s)	Appends the specified CharSequence to this sequence.
append(CharSequence s, int start, int end)	Appends a subsequence of the specified CharSequence to this sequence.
append(double d)	Appends the string representation of the double argument to this sequence.
append(float f)	Appends the string representation of the float argument to this sequence.
append(int i)	Appends the string representation of the int argument to this sequence.
append(long lng)	Appends the string representation of the long argument to this sequence.
append(Object obj)	Appends the string representation of the Object argument.
append(String str)	Appends the specified string to this character sequence.
append(StringBuffer sb)	Appends the specified StringBuffer to this sequence.
appendCodePoint(int codePoint)	Appends the string representation of the codePoint argument to this sequence.
capacity()	Returns the current capacity.
trimToSize()	Attempts to reduce storage used for the character sequence.
charAt(int index)	Returns the char value in this sequence at the specified index.
codePointAt(int index)	Returns the character (Unicode code point) at the specified index.
codePointBefore(int index)	Returns the character (Unicode code point) before the specified index.
codePointCount(int beginIndex, int endIndex)	Returns the number of Unicode code points in the specified text range of this sequence.

delete(int start, int end)	Removes the characters in a substring of this sequence.
deleteCharAt(int index)	Removes the char at the specified position in this sequence.
ensureCapacity(int minimumCapacity)	Ensures that the capacity is at least equal to the specified minimum.
getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)	Characters are copied from this sequence into the destination character array dst.
toString()	Returns a string representing the data in this sequence.
indexOf(String str)	Returns the index within this string of the first occurrence of the specified substring.
indexOf(String str, int fromIndex)	Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
insert(int offset, boolean b)	Inserts the string representation of the boolean argument into this sequence.
insert(int offset, char c)	Inserts the string representation of the char argument into this sequence.
insert(int offset, char[] str)	Inserts the string representation of the char array argument into this sequence.
insert(int index, char[] str, int offset, int len)	Inserts the string representation of a subarray of the str array argument into this sequence.
insert(int dstOffset, CharSequence s)	Inserts the specified CharSequence into this sequence.
insert(int dstOffset, CharSequence s, int start, int end)	Inserts a subsequence of the specified CharSequence into this sequence.
insert(int offset, double d)	Inserts the string representation of the double argument into this sequence.
insert(int offset, float f)	Inserts the string representation of the float argument into this sequence.
insert(int offset, long l)	Inserts the string representation of the long argument into this sequence.
insert(int offset, Object obj)	Inserts the string representation of the Object argument into this character sequence.
insert(int offset, String str)	Inserts the string into this character sequence.
lastIndexOf(String str)	Returns the index within this string of the rightmost occurrence of the specified substring.
lastIndexOf(String str, int fromIndex)	Returns the index within this string of the last occurrence of the specified substring.
length()	Returns the length (character count).
offsetByCodePoints(int index, int codePointOffset)	Returns the index within this sequence that is offset from the given index by codePointOffset code points.

replace(int start, int end, String str)	Replaces the characters in a substring of this sequence with characters in the specified String.
reverse()	Causes this character sequence to be replaced by the reverse of the sequence.
setCharAt(int index, char ch)	The character at the specified index is set to ch.
setLength(int newLength)	Sets the length of the character sequence.
subSequence(int start, int end)	Returns a new character sequence that is a subsequence of this sequence.
substring(int start)	Returns a new String that contains a subsequence of characters currently contained in this character sequence.
substring(int start, int end)	Returns a new String that contains a subsequence of characters currently contained in this sequence.

Example 15.11: Length and capacity of a string

// StringBuffer length vs. capacity.

class StringBufferDemo {

public static void main(String args[]) {

StringBuffer sb = new StringBuffer("Hello");

System.out.println("String = " + sb);

System.out.println("Length = " + sb.length());

System.out.println("Capacity = " + sb.capacity());

}

Here is the output of this program:

String = Hello

length = 5

capacity = 21

Note:

Since sb is initialized with the string "Hello" when it is created, its length is 5. Its capacity is 21 because room for 16 additional characters is automatically added.

Example 15.12: Modifying a string

The following example demonstrates charAt( ) and setCharAt( ) to modify a string object:

// Demonstrate charAt() and setCharAt().

class setCharAtDemo {

public static void main(String args[]) {

StringBuffer sb = new StringBuffer("Hello");

System.out.println("Suffer before = " + sb);

System.out.println("charAt(1) before = " + sb.charAt(1));

sb.setCharAt(1, 'i');

sb.setLength(2);

System.out.println("buffer after = " + sb);

System.out.println("charAt(1) after = " + sb.charAt(1));

}

Here is the output generated by this program:

Suffer before = Hello

charAt(1) before = e

String after = Hi

charAt(1) after = i

Example 15.13: Merging strings of StringBuffer

The append( ) method concatenates the string representation of any other type of data to the end of the invoking StringBuffer object. It has several overloaded versions. Here are a few of its forms:

StringBuffer append(String str)

StringBuffer append(int num)

StringBuffer append(Object obj)

The string representation of each parameter is obtained, often by calling String.valueOf( ). The result is appended to the current StringBuffer object. The buffer itself is returned by each version of append( ). This allows subsequent calls to be chained together, as shown in the following example:

// Demonstrate append().

class AppendDemo {

public static void main(String args[]) {

String s;

int a = 42;

StringBuffer sb = new StringBuffer(40);

s = sb.append("a =").append(a).append("!").toString();

System.out.println(s);

}

The output of this example is shown here:

a = 42!

Example 15.14: Merging strings of String and StringBuffer

Following example illustrates how StringBuffer is faster than the String class with reference to the concatenate operation.

public class ConcatTest{

public static String concatWithString() {

String t = "Java";

for (int i=0; i<10000; i++){

t = t + "Tpoint";

}

return t;

}

public static String concatWithStringBuffer(){

StringBuffer sb = new StringBuffer("Java");

for (int i=0; i<10000; i++){

sb.append("Tpoint");

}

return sb.toString();

}

public static void main(String[] args){

long startTime = System.currentTimeMillis();

concatWithString();

System.out.println("Time taken by Concating with String: "+(System.currentTimeMillis()-startTime)+"ms");

startTime = System.currentTimeMillis();

concatWithStringBuffer();

System.out.println("Time taken by Concating with StringBuffer: "+(System.currentTimeMillis()-startTime)+"ms");

}

Example 15.15: Insert character to a string

The insert( ) method inserts one string into another. It is overloaded to accept values of all the primitive types, plus Strings, Objects, and CharSequences. Like append( ), it obtains the string representation of the value it is called with. This string is then inserted into the invoking StringBuffer object. These are a few of its forms:

StringBuffer insert(int index, String str)

StringBuffer insert(int index, char ch)

StringBuffer insert(int index, Object obj)

Here, index specifies the index at which point the string will be inserted into the invoking StringBuffer object.

The following sample program inserts "like" between "I" and "Java":

// Demonstrate insert().

class insertDemo {

public static void main(String args[]) {

StringBuffer sb = new StringBuffer("I Java!");

sb.insert(2, "like ");

System.out.println(sb);

}

Example 15.16: Reversing a string

You can reverse the characters within a StringBuffer object using reverse( ), shown here: This method returns the reverse of the object on which it was called. The following program demonstrates reverse( ).

// Using reverse() to reverse a StringBuffer.

class StringReverseDemo {

public static void main(String args[]) {

StringBuffer s = new StringBuffer("abcdef");

System.out.println(s);

s.reverse();

System.out.println(s);

}

Example 15.17: String modification

Here is a program that demonstrates the delete( ) and deleteCharAt( ) methods:

// Demonstrate delete() and deleteCharAt()

class StringDeleteDemo {

public static void main(String args[]) {

StringBuffer sb = new StringBuffer("This is a test.");

sb.delete(4, 7);

System.out.println("After delete: " + sb);

sb.deleteCharAt(0);

System.out.println("After deleteCharAt: " + sb);

}

The following output is produced:

After delete: This a test.

After deleteCharAt: his a test.

Example 15.18: Replacing a string

You can replace one set of characters with another set inside a StringBuffer object by calling replace( ). The following program demonstrates replace( ):

// Demonstrate replace()

class replaceDemo {

public static void main(String args[]) {

StringBuffer sb = new StringBuffer("This is a test.");

sb.replace(5, 7, "was");

System.out.println("After replace: " + sb);

}

Here is the output:

After replace: This was a test.

Example 15.19: Substring of a string

You can obtain a portion of a StringBuffer by calling substring( ). It has the following two forms:

String substring(int startIndex)

String substring(int startIndex, int endIndex)

The first form returns the substring that starts at startIndex and runs to the end of the invoking StringBuffer object. The second form returns the substring that starts at startIndex and runs through endIndex–1. These methods work just like those defined for String that were described earlier. The following program demonstrates indexOf( ) and lastIndexOf( ):

class IndexOfDemo {

public static void main(String args[]) {

StringBuffer sb = new StringBuffer("one two one");

int i;

i = sb.indexOf("one");

System.out.println("First index: " + i);

i = sb.lastIndexOf("one");

System.out.println("Last index: " + i);

}

Example 15.20: hashCode( ) of a string

public class InstanceTest{

public static void main(String args[]){

System.out.println("Hashcode test of String:");

String str="java";

System.out.println(str.hashCode());

str=str+"tpoint";

System.out.println(str.hashCode());

System.out.println("Hashcode test of StringBuffer:");

StringBuffer sb=new StringBuffer("java");

System.out.println(sb.hashCode());

sb.append("tpoint");

System.out.println(sb.hashCode());

}

Example 15.21: String to other forms

Methods toBinaryString( ), toHexString( ), and toOctalString( ), which convert a value into a binary, hexadecimal, or octal string, respectively. The following program demonstrates binary, hexadecimal, and octal conversion:

// Convert an integer into binary, hexadecimal, and octal.

class StringConversions {

public static void main(String args[]) {

int num = 19648;

System.out.println(num + " in binary: " +

Integer.toBinaryString(num));

System.out.println(num + " in octal: " +

Integer.toOctalString(num));

System.out.println(num + " in hexadecimal: " +

Integer.toHexString(num));

}

The output of this program is shown here:

19648 in binary: 100110011000000

19648 in octal: 46300

19648 in hexadecimal: 4cc0

StringBuilder

Introduced by JDK 5, StringBuilder is a relatively recent addition to Java’s string handling capabilities. StringBuilder is similar to StringBuffer except for one important difference: it is not synchronized, which means that it is not thread-safe. The advantage of StringBuilder is faster performance. However, in cases in which a mutable string will be accessed by multiple threads, and no external synchronization is employed, you must use StringBuffer rather than StringBuilder.

StringTokenizer

• The processing of text often consists of parsing a formatted input string. Parsing is the division of text into a set of discrete parts, or tokens, which in a certain sequence can convey a semantic meaning.

• The StringTokenizer class provides the first step in this parsing process, often called the lexer (lexical analyzer) or scanner.

• StringTokenizer implements the Enumeration interface.

• Therefore, given an input string, you can enumerate the individual tokens contained in it using StringTokenizer.

The StringTokenizer constructors are shown here:

Method	Description
StringTokenizer(String str)	Constructs a string tokenizer for the specified string.
StringTokenizer(String str, String delim)	Constructs a string tokenizer for the specified string.
StringTokenizer(String str, String delim, boolean returnDelims)	Constructs a string tokenizer for the specified string.

The StringTokenizer methods are shown here:

Method	Description
countTokens()	Calculates the number of times that this tokenizer's nextToken method can be called before it generates an exception.
hasMoreElements()	Returns the same value as the hasMoreTokens method.
hasMoreTokens()	Tests if there are more tokens available from this tokenizer's string.
nextElement()	Returns the same value as the nextToken method, except that its declared return value is Object rather than String.
nextToken()	Returns the next token from this string tokenizer.
nextToken(String delim)	Returns the next token in this string tokenizer's string.

In all versions, str is the string that will be tokenized. In the first version, the default delimiters are used. In the second and third versions, delimiters is a string that specifies the delimiters. In the third version, if delimAsToken is true, then the delimiters are also returned as tokens when the string is parsed. Otherwise, the delimiters are not returned. Delimiters are not returned as tokens by the first two forms.

Once you have created a StringTokenizer object, the nextToken( ) method is used to extract consecutive tokens. The hasMoreTokens( ) method returns true while there are more tokens to be extracted. Since StringTokenizer implements Enumeration, the hasMoreElements( ) and nextElement( ) methods are also implemented, and they act the same as hasMoreTokens( ) and nextToken( ), respectively.

Example 15.22: String to other forms

Here is an example that creates a StringTokenizer to parse "key=value" pairs. Consecutive sets of "key=value" pairs are separated by a semicolon.

// Demonstrate StringTokenizer.

import java.util.StringTokenizer;

class StringTokenizerDemo{

static String in = "Title=Data Structures Using Java;" +

"Author=Debasis Samanta;" + "Publisher=NPTEL;" + "Copyright=2020";

public static void main(String args[]) {

StringTokenizer st = new StringTokenizer(in, "=;");

while(st.hasMoreTokens()) {

String key = st.nextToken();

String val = st.nextToken();

System.out.println(key + "\t" + val);

}

The output from this program is shown here:

Title Data Structures Using Java

Author Debasis Samanta

Publisher NPTEL

Miscellaneous Utilities

Date

The Date class encapsulates the current date and time. When Java 1.1 was released, many of the functions carried out by the original Date class were moved into the Calendar and DateFormat classes, and as a result, many of the original 1.0 Date methods were deprecated.

Constructors defined by class Date

Constructor	Description
Date()	Creates date object representing current date and time.
Date(long date)	Allocates a Date object and initializes it to represent the specified number of milliseconds since the standard base time known as "the epoch", namely January 1, 1970, 00:00:00 GMT.
Date(int year, int month, int date)	Create a date with the specific data as yyyy/mm/dd.
Date(int year, int month, int date, int hrs, int min)	Create a date with the specific data with time.
Date(int year, int month, int date, int hrs, int min, int sec)	Create a date with the specific data with detailed time.
Date(String s)	Create a date with the specific data as a string.

The first constructor initializes the object with the current date and time. The second constructor accepts one argument that equals the number of milliseconds that have elapsed since midnight, January 1, 1970. The last four constructors are currently being deprecated.

Example 17.1: Creating objects of Date class

The following program demonstrates, how to obtain the date and time in terms of milliseconds, in its default string representation as returned by toString( ), or (beginning with JDK 8) as an Instant object. To obtain more-detailed information about the date and time, you will use the Calendar class.

// Show date and time using only Date methods.

import java.util.Date;

class CreateDateDemo {

public static void main(String args[]) {

// Creating an instantiate a Date object

Date date1 = new Date(); // Create an object of the current date

// Display time and date using toString()

System.out.println(“Current date: “ + date1);

Date date2 = new Date(2323223232L);

System.out.println("Your date is: "+ date2 );

// Create a date object with specific data

Date date3 = new Date(1965, 1, 12);

System.out.println("Another date is: "+ date3 );

}

Sample output is shown here:

Current date: Sun Mar 01 08:13:24 CST 2020

Your date is: Wed Jan 28 02:50:23 IST 1970

Another date is: Mon Jan 12 00:00:00 IST 1964

Methods defined by class Date

The nondeprecated methods defined by Date are shown in Table below. Date also implements the Comparable interface. The table lists only the non-deprecated methods.

Method	Description
after(Date when)	Tests if this date is after the specified date.
before(Date when)	Tests if this date is before the specified date.
clone()	Return a copy of this object.
compareTo(Date anotherDate)	Compares two Dates for ordering.
equals(Object obj)	Compares two dates for equality.
from(Instant instant)	Obtains an instance of Date from an Instant object.
getTime()	Returns the number of milliseconds since January 1, 1970, 00:00:00 GMT represented by this Date object.
hashCode()	Returns a hash code value for this object.
setTime(long time)	Sets this Date object to represent a point in time that is time milliseconds after January 1, 1970 00:00:00 GMT.
toInstant()	Converts this Date object to an Instant.
toString()	Converts this Date object to a String form.

Example 17.2: Simple examples of date objects

// Show date and time using only Date methods.

import java.util.Date;

class UseDateDemo {

public static void main(String args[]) {

// Creating date objects

Date d1 = new Date(2000, 11, 21);

Date d2 = new Date(); // Current date

Date d3 = new Date(2010, 1, 3);

boolean a = d3.after(d1);

System.out.println("Date d3 comes after " +

"date d2: " + a);

boolean b = d3.before(d2);

System.out.println("Date d3 comes before "+

"date d2: " + b);

int c = d1.compareTo(d2);

System.out.println(c);

// Display number of milliseconds since midnight, January 1, 1970 GMT

System.out.println("Miliseconds from Jan 1 "+

"1970 to date d1 is " + d1.getTime());

System.out.println("Before setting "+d2.toString());

d2.setTime(204587433443L);

System.out.println("After setting "+d2.toString());

}

Sample output is shown here:

Date d3 comes after date d2: true

Date d3 comes before date d2: false

Miliseconds from Jan 1 1970 to date d1 is 60935500800000

Before setting Tue Jul 12 13:13:16 UTC 2016

After setting Fri Jun 25 21:50:33 UTC 1976

Example 17.3: Another example of date class

import java.util.*;

public class DateChangeDemo {

public static void main(String args[]) {

try {

System.out.println(new Date( ) + "\n");

Thread.sleep(5*60*10);

System.out.println(new Date( ) + "\n");

} catch (Exception e) {

System.out.println("Got an exception!");

}

Sample output is shown here:

Fri Apr 10 18:04:41 GMT 2020

Fri Apr 10 18:04:51 GMT 2020

Example 17.4: Measuring elapsed time between two dates

import java.util.*;

public class ElapsedTimeDemo {

public static void main(String args[]) {

try {

long start = System.currentTimeMillis( );

System.out.println(new Date( ) + "\n");

Thread.sleep(5*60*10);

System.out.println(new Date( ) + "\n");

long end = System.currentTimeMillis( );

long diff = end - start;

System.out.println("Difference is : " + diff);

} catch (Exception e) {

System.out.println("Got an exception!");

}

Sample output is shown here:

Fri Apr 10 18:16:51 GMT 2020

Fri Apr 10 18:16:57 GMT 2020

Difference is : 5993

Calendar

The abstract Calendar class provides a set of methods that allows you to convert a time in milliseconds to a number of useful components. The type of information that can be provided are:

• Year

• Month

• Day

• Hour

• Minute

• Second

It is intended that subclasses of Calendar will provide the specific functionality to interpret time information according to their own rules. An example of such a subclass is GregorianCalendar.

Note: JDK 8 defines a new date and time API in java.time, which new applications may want to employ.

Constructors defined by class Calendar

Calendar provides no public constructors.

Methods defined by class Calendar

A sampling of methods defined by Calendar are shown in table below.

	Method		Description
	add(int field, int amount)		Adds or subtracts the specified amount of time to the given calendar field, based on the calendar's rules.
	after(Object when)		Returns whether this Calendar represents a time after the time represented by the specified Object.
	before(Object when)		Returns whether this Calendar represents a time before the time represented by the specified Object.
	clear()		Sets all the calendar field values and the time value (millisecond offset from the Epoch) of this Calendar undefined.
	clear(int field)		Sets the given calendar field value and the time value (millisecond offset from the Epoch) of this Calendar undefined.
	clone()		Creates and returns a copy of this object.
	compareTo(Calendar anotherCalendar)		Compares the time values (millisecond offsets from the Epoch) represented by two Calendar objects.
	complete()		Fills in any unset fields in the calendar fields.
	computeFields()		Converts the current millisecond time value time to calendar field values in fields[].
computeTime()		Converts the current calendar field values in fields[] to the millisecond time value time.
equals(Object obj)		Compares this Calendar to the specified Object.
get(int field)		Returns the value of the given calendar field.
getActualMaximum(int field)		Returns the maximum value that the specified calendar field could have, given the time value of this Calendar.
getActualMinimum(int field)		Returns the minimum value that the specified calendar field could have, given the time value of this Calendar.
getAvailableLocales()		Returns an array of all locales for which the getInstance methods of this class can return localized instances.
getDisplayName(int field, int style, Locale locale)		Returns the string representation of the calendar field value in the given style and locale.
getDisplayNames(int field, int style, Locale locale)		Returns a Map containing all names of the calendar field in the given style and locale and their corresponding field values.
getFirstDayOfWeek()		Gets what the first day of the week is; e.g., SUNDAY in the U.S., MONDAY in France.
getGreatestMinimum(int field)		Returns the highest minimum value for the given calendar field of this Calendar instance.
getInstance()		Gets a calendar using the default time zone and locale.
getInstance(Locale aLocale)		Gets a calendar using the default time zone and specified locale.
getInstance(TimeZone zone)		Gets a calendar using the specified time zone and default locale.
getInstance(TimeZone zone, Locale aLocale)		Gets a calendar with the specified time zone and locale.
getLeastMaximum(int field)		Returns the lowest maximum value for the given calendar field of this Calendar instance.
getMaximum(int field)		Returns the maximum value for the given calendar field of this Calendar instance.
getMinimalDaysInFirstWeek()		Gets what the minimal days required in the first week of the year are;
getMinimum(int field)		Returns the minimum value for the given calendar field of this Calendar instance.
getTime()		Returns a Date object representing this Calendar's time value (millisecond offset from the Epoch").
getTimeInMillis()		Returns this Calendar's time value in milliseconds.
setWeekDate(int weekYear, int weekOfYear, int dayOfWeek)		Sets the date of this Calendar with the the given date specifiers - week year, week of year, and day of week.
getTimeZone()		Gets the time zone.
getWeeksInWeekYear()		Returns the number of weeks in the week year represented by this Calendar.
getWeekYear()		Returns the week year represented by this Calendar.
hashCode()		Returns a hash code for this calendar.
internalGet(int field)		Returns the value of the given calendar field.
isLenient()		Tells whether date/time interpretation is to be lenient.
isSet(int field)		Determines if the given calendar field has a value set, including cases that the value has been set by internal fields calculations triggered by a get method call.
isWeekDateSupported()		Returns whether this Calendar supports week dates.
roll(int field, boolean up)		Adds or subtracts (up/down) a single unit of time on the given time field without changing larger fields.
roll(int field, int amount)		Adds the specified (signed) amount to the specified calendar field without changing larger fields.
toString()		Return a string representation of this calendar.
set(int field, int value)		Sets the given calendar field to the given value.
set(int year, int month, int date)		Sets the values for the calendar fields YEAR, MONTH, and DAY_OF_MONTH.
set(int year, int month, int date, int hourOfDay, int minute)		Sets the values for the calendar fields YEAR, MONTH, DAY_OF_MONTH, HOUR_OF_DAY, and MINUTE.
set(int year, int month, int date, int hourOfDay, int minute, int second)		Sets the values for the fields YEAR, MONTH, DAY_OF_MONTH, HOUR, MINUTE, and SECOND.
setFirstDayOfWeek(int value)		Sets what the first day of the week is; e.g., SUNDAY in the U.S., MONDAY in France.
setLenient(boolean lenient)		Specifies whether or not date/time interpretation is to be lenient.
setMinimalDaysInFirstWeek(int value)		Sets what the minimal days required in the first week of the year are;
setTime(Date date)		Sets this Calendar's time with the given Date.
setTimeInMillis(long millis)		Sets this Calendar's current time from the given long value.
setTimeZone(TimeZone value)		Sets the time zone with the given time zone value.

Fields defined by class Calendar

Calendar defines the following int constants, which are used when you get or set components of the calendar. (The ones with the suffix FORMAT or STANDALONE were added by JDK 8.)

ALL_STYLES	DST_OFFSET	JULY	SATURDAY	WEEK_OF_YEAR
AM	ERA	JUNE	SECOND	YEAR
AM_PM	FEBRUARY	LONG	SEPTEMBER	ZONE_OFFSET
APRIL	FIELD_COUNT	MARCH	SHORT	PM
areFieldsSet	fields	MAY	SUNDAY	DECEMBER
AUGUST	FRIDAY	MILLISECOND	THURSDAY	JANUARY
DATE	HOUR	MINUTE	time	OCTOBER
DAY_OF_WEEK	HOUR_OF_DAY	MONDAY	TUESDAY	WEEK_OF_MONTH
DAY_OF_WEEK_IN_MONTH	isSet	MONTH	UNDECIMBER
DAY_OF_YEAR	isTimeSet	NOVEMBER	WEDNESDAY

Note:

areFieldsSet is a boolean that indicates if the time components have been set. fields is an array of ints that holds the components of the time. isSet is a boolean array that indicates if a specific time component has been set. time is a long that holds the current time for this object. isTimeSet is a boolean that indicates if the current time has been set.

Example 17.5: Illustration of calendar objects

The following program demonstrates several Calendar methods:

import java.util.Calendar;

class CalendarDemo {

public static void main(String args[]) {

// Set months in your calendar

String months[] = {"Jan", "Feb", "Mar", "Apr","May", "Jun", "Jul", "Aug",

"Sep", "Oct", "Nov", "Dec"};

/* Get an instance of a calendar initialized with the current date and time in the default locale and time zone. */

Calendar calendar = Calendar.getInstance();

// Display current time and date information.

System.out.print("Date: ");

System.out.print(months[calendar.get(Calendar.MONTH)]);

System.out.print(" " + calendar.get(Calendar.DATE) + " ");

System.out.println(calendar.get(Calendar.YEAR));

System.out.print("Time: ");

System.out.print(calendar.get(Calendar.HOUR) + ":");

System.out.print(calendar.get(Calendar.MINUTE) + ":");

System.out.println(calendar.get(Calendar.SECOND));

// Set the time and date information and display it.

calendar.set(Calendar.HOUR, 10);

calendar.set(Calendar.MINUTE, 29);

calendar.set(Calendar.SECOND, 22);

System.out.print("Updated time: ");

System.out.print(calendar.get(Calendar.HOUR) + ":");

System.out.print(calendar.get(Calendar.MINUTE) + ":");

System.out.println(calendar.get(Calendar.SECOND));

// Getting certain information about the calendar object

int max = calendar.getMaximum(Calendar.DAY_OF_WEEK);

System.out.println("Maximum number of days in a week: " + max);

max = calendar.getMaximum(Calendar.WEEK_OF_YEAR);

System.out.println("Maximum number of weeks in a year: " + max);

// Seeting for an updated in the instance of the calendar

calendar.add(Calendar.DATE, -15);

System.out.println("15 days ago: " + calendar.getTime());

calendar.add(Calendar.MONTH, 4);

System.out.println("4 months later: " + calendar.getTime());

calendar.add(Calendar.YEAR, 2);

System.out.println("2 years later: " + calendar.getTime());

}

Sample output is shown here:

Date: Jan 1 2014

Time: 11:29:39

Updated time: 10:29:22

Maximum number of days in a week: 7

Maximum number of weeks in a year: 53

15 days ago: Mon Aug 13 11:10:57 UTC 2018

4 months later: Thu Dec 13 11:10:57 UTC 2018

2 years later: Sun Dec 13 11:10:57 UTC 2020

GregorianCalendar

GregorianCalendar is a concrete implementation of a Calendar that implements the normal Gregorian calendar with which you are familiar. The getInstance( ) method of Calendar will typically return a GregorianCalendar initialized with the current date and time in the default locale and time zone. GregorianCalendar defines two fields: AD and BC. These represent the two eras defined by the Gregorian calendar.

Constructors defined by class GregorianCalendar

There are also several constructors for GregorianCalendar objects. The default, GregorianCalendar(), initializes the object with the current date and time in the default locale and time zone. Three more constructors offer increasing levels of specificity. All three versions set the day, month, and year. Here, year specifies the year. The month is specified by month, with zero indicating January. The day of the month is specified by dayOfMonth. The first version sets the time to midnight. The second version also sets the hours and the minutes. The third version adds seconds.

Constructor	Description
GregorianCalendar()	Constructs a default GregorianCalendar using the current time in the default time zone with the default locale.
GregorianCalendar(int year, int month, int dayOfMonth)	Constructs a GregorianCalendar with the given date set in the default time zone with the default locale.
GregorianCalendar(int year, int month, int dayOfMonth, int hourOfDay, int minute)	Constructs a GregorianCalendar with the given date and time set for the default time zone with the default locale.
GregorianCalendar(int year, int month, int dayOfMonth, int hourOfDay, int minute, int second)	Constructs a GregorianCalendar with the given date and time set for the default time zone with the default locale.
GregorianCalendar(Locale aLocale)	Constructs a GregorianCalendar based on the current time in the default time zone with the given locale.
GregorianCalendar(TimeZone zone)	Constructs a GregorianCalendar based on the current time in the given time zone with the default locale.
GregorianCalendar(TimeZone zone, Locale aLocale)	Constructs a GregorianCalendar based on the current time in the given time zone with the given locale.

Methods defined by class GregorianCalendar

GregorianCalendar provides an implementation of all the abstract methods in Calendar. It also provides some additional methods. Perhaps the most interesting is isLeapYear( ), which tests if the year is a leap year. Its form is boolean isLeapYear(int year) This method returns true if year is a leap year and false otherwise. JDK 8 also adds the following methods: from( ) and toZonedDateTime( ), which support the new date and time API, and getCalendarType( ), which returns the calendar type as a string, which is “gregory”. The following program demonstrates GregorianCalendar:

Example 17.6: Illustration of Gregorian calendar objects

// Demonstrate GregorianCalendar

import java.util.*;

class GregorianCalendarDemo {

public static void main(String args[]) {

String months[] = {"Jan", "Feb", "Mar", "Apr",

"May", "Jun", "Jul", "Aug",

"Sep", "Oct", "Nov", "Dec"};

int year;

/* Create a Gregorian calendar initialized with the current date and time in the

default locale and timezone. */

GregorianCalendar gcalendar = new GregorianCalendar();

// Display current time and date information.

System.out.print("Date: ");

System.out.print(months[gcalendar.get(Calendar.MONTH)]);

System.out.print(" " + gcalendar.get(Calendar.DATE) + " ");

System.out.println(year = gcalendar.get(Calendar.YEAR));

System.out.print("Time: ");

System.out.print(gcalendar.get(Calendar.HOUR) + ":");

System.out.print(gcalendar.get(Calendar.MINUTE) + ":");

System.out.println(gcalendar.get(Calendar.SECOND));

// Test if the current year is a leap year

if(gcalendar.isLeapYear(year)) {

System.out.println("The current year is a leap year");

}

else {

System.out.println("The current year is not a leap year");

}

Sample output is shown here:

Date: Jan 1 2014

Time: 1:45:5

The current year is not a leap year

TimeZone

We divide the whole earth east to west into 24 different regions based on longitude so each region is 15 degrees wider. “Time Zone” is used to describe the current time for different areas of the world. It refers to one of the specific regions out of the 24 total regions in the world that are divided up by longitude. So, there are 24 different Time zones available on earth. Each time zone is 15 degrees wide and there’s a one-hour difference between each one.

· Within each one of those regions, a standard version of time is maintained. The different time zones are calculated based on their relation to the coordinated universal time or UTC (also referred to as Greenwich Mean Time (GMT)).

Depending on the distance east or west from the Greenwich Meridian you must either add or subtract the appropriate time for every 15-degree interval in Longitude.
To find the time zone in hours of a particular location, you can take the longitude in degrees and divide it by 15. For example, 120° E would be 120/15 which equals 8. That translates to the time zone being 7 hours ahead of UTC or GMT time, which can also be labelled as UTC+8. Where 8 is a time offset for that location.
A time offset is an amount of time subtracted from or added to universal time to get the current civil time, whether it is standard time or daylight-saving time (DST).

The abstract TimeZone class allows you to work with time zone offsets from Greenwich mean time (GMT).

The Java TimeZone class is a class that represents time zones, and is helpful when doing calendar arithmetics across time zones. The java.util.TimeZone class is used in conjunction with the java.util.Calendar class.

Constructors

TimeZone only supplies the default constructor.

A sampling of methods defined by TimeZone is given in the following table.

Method	Description
clone()	Creates a copy of this TimeZone.
getAvailableIDs()	Gets all the available IDs supported.
getAvailableIDs(int rawOffset)	Gets the available IDs according to the given time zone offset in milliseconds.
getDefault()	Gets the default TimeZone for this host.
getDisplayName()	Returns a long standard time name of this TimeZone suitable for presentation to the user in the default locale.
getDisplayName(boolean daylight, int style)	Returns a name in the specified style of this TimeZone suitable for presentation to the user in the default locale.
getDisplayName(boolean daylight, int style, Locale locale)	Returns a name in the specified style of this TimeZone suitable for presentation to the user in the specified locale.
getDisplayName(Locale locale)	Returns a long standard time name of this TimeZone suitable for presentation to the user in the specified locale.
getDSTSavings()	Returns the amount of time to be added to local standard time to get local wall clock time.
getID()	Gets the ID of this time zone.
getOffset(int era, int year, int month, int day, int dayOfWeek, int milliseconds)	Gets the time zone offset, for current date, modified in case of daylight savings.
getOffset(long date)	Returns the offset of this time zone from UTC at the specified date.
getRawOffset()	Returns the amount of time in milliseconds to add to UTC to get standard time in this time zone.
getTimeZone(String ID)	Gets the TimeZone for the given ID.
hasSameRules(TimeZone other)	Returns true if this zone has the same rule and offset as another zone.
inDaylightTime(Date date)	Queries if the given date is in Daylight Saving Time in this time zone.
observesDaylightTime()	Returns true if this TimeZone is currently in Daylight Saving Time
setDefault(TimeZone zone)	Sets the TimeZone that is returned by the getDefault method.
setID(String ID)	Sets the time zone ID.
setRawOffset(int offsetMillis)	Sets the base time zone offset to GMT.
useDaylightTime()	Queries if this TimeZone uses Daylight Saving Time.

Example 17.7: Illustration of time zone objects

import java.util.*;

public class TimeZoneExample {

public static void main( String args[] ){

String[] zoneIds = TimeZone.getAvailableIDs(); // Ids of all time zones

System.out.println(“Total time zones on the earth: “ + zoneIds.length);

// All the timezones whose offset is 7200000 (i.e., 2 hours)

String[] timezones = TimeZone.getAvailableIDs(7200000);

System.out.print("No of Time Zone having time offset 2 hours");

System.out.println(timezones.length); // Print total no of Timezones

System.out.println("In TimeZone class available Ids are: ");

for (int i=0; i<timezones.length; i++){

System.out.println(timezones[i]);

}

TimeZone zone = TimeZone.getTimeZone("Asia/Kolkata");

System.out.println("The Offset value of TimeZone: " +

zone.getOffset(Calendar.ZONE_OFFSET));

String name = zone.getDisplayName();

System.out.println("Name of the time zone: "+ name);

}

Sample output is shown here:

Total time zones on the earth: 628

No of Time Zone having time offset 2 hours: 43

In TimeZone class available Ids are:

Africa/Abidjan

Africa/Accra

Africa/Addis_Ababa

Africa/Algiers

Africa/Asmara

Africa/Asmera

Africa/Bamako

Africa/Bangui

Africa/Banjul

Africa/Bissau

...and so on ....

The Offset value of TimeZone: 19800000

Name of the time zone: India Standard Time

SimpleTimeZone

The SimpleTimeZone class is a convenient subclass of TimeZone. It implements TimeZone's abstract methods and allows you to work with time zones for a Gregorian calendar. It also computes daylight saving time.

SimpleTimeZone defines four constructors.

Constructor	Description
SimpleTimeZone(int rawOffset, String ID)	Constructs a SimpleTimeZone with the given base time zone offset from GMT and time zone ID with no daylight saving time schedule.
SimpleTimeZone(int rawOffset, String ID, int startMonth, int startDay, int startDayOfWeek, int startTime, int endMonth, int endDay, int endDayOfWeek, int endTime)	Constructs a SimpleTimeZone with the given base time zone offset from GMT, time zone ID, and rules for starting and ending the daylight time.
SimpleTimeZone(int rawOffset, String ID, int startMonth, int startDay, int startDayOfWeek, int startTime, int endMonth, int endDay, int endDayOfWeek, int endTime, int dstSavings)	Constructs a SimpleTimeZone with the given base time zone offset from GMT, time zone ID, and rules for starting and ending the daylight time.
SimpleTimeZone(int rawOffset, String ID, int startMonth, int startDay, int startDayOfWeek, int startTime, int startTimeMode, int endMonth, int endDay, int endDayOfWeek, int endTime, int endTimeMode, int dstSavings)	Constructs a SimpleTimeZone with the given base time zone offset from GMT, time zone ID, and rules for starting and ending the daylight time.

Here, time0mode specifies the mode of the starting time, and time1mode specifies the mode of the ending time. Valid mode values include:

Field	Description
STANDARD_TIME	Constant for a mode of start or end time specified as standard time.
UTC_TIME	Constant for a mode of start or end time specified as UTC.
WALL_TIME	Constant for a mode of start or end time specified as wall clock time.

The time mode indicates how the time values are interpreted. The default mode used by the other constructors is WALL_TIME.

Method	Description
clone()	Returns a clone of this SimpleTimeZone instance.
equals(Object obj)	Compares the equality of two SimpleTimeZone objects.
getDSTSavings()	Returns the amount of time in milliseconds that the clock is advanced during daylight saving time.
getOffset(int era, int year, int month, int day, int dayOfWeek, int millis)	Returns the difference in milliseconds between local time and UTC, taking into account both the raw offset and the effect of daylight saving, for the specified date and time.
getOffset(long date)	Returns the offset of this time zone from UTC at the given time.
getRawOffset()	Gets the GMT offset for this time zone.
hashCode()	Generates the hash code for the SimpleDateFormat object.
hasSameRules(TimeZone other)	Returns true if this zone has the same rules and offset as another zone.
inDaylightTime(Date date)	Queries if the given date is in daylight saving time.
observesDaylightTime()	Returns true if this SimpleTimeZone observes Daylight Saving Time.
setDSTSavings(int millisSavedDuringDST)	Sets the amount of time in milliseconds that the clock is advanced during daylight saving time.
setEndRule(int endMonth, int endDay, int endTime)	Sets the daylight saving time end rule to a fixed date within a month.
setEndRule(int endMonth, int endDay, int endDayOfWeek, int endTime)	Sets the daylight saving time end rule.
setEndRule(int endMonth, int endDay, int endDayOfWeek, int endTime, boolean after)	Sets the daylight saving time end rule to a weekday before or after the given date within a month, e.g., the first Monday on or after the 8th.
setRawOffset(int offsetMillis)	Sets the base time zone offset to GMT.
setStartRule(int startMonth, int startDay, int startTime)	Sets the daylight saving time start rule to a fixed date within a month.
setStartRule(int startMonth, int startDay, int startDayOfWeek, int startTime)	Sets the daylight saving time start rule.
setStartRule(int startMonth, int startDay, int startDayOfWeek, int startTime, boolean after)	Sets the daylight saving time start rule to a weekday before or after the given date within a month, e.g., the first Monday on or after the 8th.
setStartYear(int year)	Sets the daylight saving time starting year.
toString()	Returns a string representation of this time zone.
useDaylightTime()	Queries if this time zone uses daylight saving time.

Locale

The Locale class is instantiated to produce objects that describe a geographical or cultural region. It is one of several classes that provide you with the ability to write programs that can execute in different international environments. The formats used to display dates, times, and numbers are different in various regions. Internationalization is a large topic that is beyond the scope of this course. However, many programs will only need to deal with its basics, which include setting the current locale. The Locale class defines the following constants that are useful for dealing with several common locales:

Constructors of this class are:

Constructor	Description
Locale(String language)	Construct a locale from a language code.
Locale(String language, String country)	Construct a locale from language and country.
Locale(String language, String country, String variant)	Construct a locale from language, country and variant.

Methods of this class are:

Method	Description
clone()	Overrides Cloneable.
equals(Object obj)	Returns true if this Locale is equal to another object.
forLanguageTag(String languageTag)	Returns a locale for the specified IETF BCP 47 language tag string.
getAvailableLocales()	Returns an array of all installed locales.
getCountry()	Returns the country/region code for this locale, which should either be the empty string, an uppercase ISO 3166 2-letter code, or a UN M.49 3-digit code.
getDefault()	Gets the current value of the default locale for this instance of the Java Virtual Machine.
getDefault(Locale.Category category)	Gets the current value of the default locale for the specified Category for this instance of the Java Virtual Machine.
getDisplayCountry()	Returns a name for the locale's country that is appropriate for display to the user.
getDisplayCountry(Locale inLocale)	Returns a name for the locale's country that is appropriate for display to the user.
getDisplayLanguage()	Returns a name for the locale's language that is appropriate for display to the user.
getDisplayLanguage(Locale inLocale)	Returns a name for the locale's language that is appropriate for display to the user.
getDisplayName()	Returns a name for the locale that is appropriate for display to the user.
getDisplayName(Locale inLocale)	Returns a name for the locale that is appropriate for display to the user.
getDisplayScript()	Returns a name for the the locale's script that is appropriate for display to the user.
getDisplayScript(Locale inLocale)	Returns a name for the locale's script that is appropriate for display to the user.
getDisplayVariant()	Returns a name for the locale's variant code that is appropriate for display to the user.
getDisplayVariant(Locale inLocale)	Returns a name for the locale's variant code that is appropriate for display to the user.
getExtension(char key)	Returns the extension (or private use) value associated with the specified key, or null if there is no extension associated with the key.
getExtensionKeys()	Returns the set of extension keys associated with this locale, or the empty set if it has no extensions.
getISO3Country()	Returns a three-letter abbreviation for this locale's country.
getISO3Language()	Returns a three-letter abbreviation of this locale's language.
getISOCountries()	Returns a list of all 2-letter country codes defined in ISO 3166.
getISOLanguages()	Returns a list of all 2-letter language codes defined in ISO 639.
getLanguage()	Returns the language code of this Locale.
getScript()	Returns the script for this locale, which should either be the empty string or an ISO 15924 4-letter script code.
getUnicodeLocaleAttributes()	Returns the set of unicode locale attributes associated with this locale, or the empty set if it has no attributes.
getUnicodeLocaleKeys()	Returns the set of Unicode locale keys defined by this locale, or the empty set if this locale has none.
getUnicodeLocaleType(String key)	Returns the Unicode locale type associated with the specified Unicode locale key for this locale.
getVariant()	Returns the variant code for this locale.
hashCode()	Override hashCode.
setDefault(Locale.Category category, Locale newLocale)	Sets the default locale for the specified Category for this instance of the Java Virtual Machine.
setDefault(Locale newLocale)	Sets the default locale for this instance of the Java Virtual Machine.
toLanguageTag()	Returns a well-formed IETF BCP 47 language tag representing this locale.
toString()	Returns a string representation of this Locale object, consisting of language, country, variant, script, and extensions.

Currency

The Currency class of java.util package simply a way to represent a currency. Currencies are identified by their ISO 4217 currency codes. Currencies can be represented in the code in two ways: a three-letter alphabetic code (e.g., INR for Indian Rupees, JPY for Japan Yen, etc.); alternatively, a three-digit numeric code are also known.

This class has been designed so that there’s never more than one Currency instance for any given currency. Because of this design, the Currency class has no public constructor. Instead, you can obtain a Currency instance using the getInstance methods. This behavior may be related to another commonly used class Calendar which follows the same principle.

The methods supported by Currency are shown in below.

Method	Description
getAvailableCurrencies()	Gets the set of available currencies.
getCurrencyCode()	Gets the ISO 4217 currency code of this currency.
getDefaultFractionDigits()	Gets the default number of fraction digits used with this currency.
getDisplayName()	Gets the name that is suitable for displaying this currency for the default DISPLAY locale.
getDisplayName(Locale locale)	Gets the name that is suitable for displaying this currency for the specified locale.
getInstance(Locale locale)	Returns the Currency instance for the country of the given locale.
getInstance(String currencyCode)	Returns the Currency instance for the given currency code.
getNumericCode()	Returns the ISO 4217 numeric code of this currency.
getSymbol()	Gets the symbol of this currency for the default DISPLAY locale.
getSymbol(Locale locale)	Gets the symbol of this currency for the specified locale.
toString()	Returns the ISO 4217 currency code of this currency.

Example 17.8: Illustration of currency objects

// The following program demonstrates Currency:

import java.util.*;

class CurrencyDemo {

public static void main(String args[]) {

Currency c;

Currency c = Currency.getInstance(Locale.US);

System.out.println("USD Symbol: " + c.getSymbol());

System.out.println("Default fractional digits: " +

c.getDefaultFractionDigits());

// Use of getInstance() methods

Currency c1 = Currency.getInstance("AUD"); //Australian Dollar

Currency c2 = Currency.getInstance("JPY"); //Japan Yen

Currency c3 = Currency.getInstance("INR"); //Indian rupees

// Use of getSymbol() method

System.out.println("AUD Symbol : "+c1.getSymbol());

System.out.println("JPY Symbol : "+c2.getSymbol());

System.out.println("INR Symbol : "+c3.getSymbol());

}

The output is shown here:

USD Symbol: $

Default fractional digits: 2

AUD Symbol: $

JPY Symbol: Y

INR Symbol: R

Java Cursors

When you are dealing with a collection, you have to perform CRUD operations. The CRUD operations in JCF implies the following.

Create: Adding new elements to Collection object.

Read: Retrieving elements from Collection object.

Update: Updating or setting existing elements in Collection object.

Delete: Removing elements from Collection object.

You will see there are many classes in the JCF loaded with many methods in each to accomplish the CRUD operations. In addition to the CRUD operations, it is also an important aspect to traverse or visit each element in the cursor. For this very reason, Java developer introduces a concept called Java cursor. A Java cursor is a pointer (more precisely loop indicator), which is used to iterate (loop or cycle or visit) or traverse or retrieve collection elements one by one. Java supports the following four different cursors.

· Enumeration

· Iterator

· ListIterator

· Spliterator

Let us learn each of the above-mentioned Java cursors, in details with appropriate illustrations.

Enumeration interface

It is an interface used to get elements of legacy collections (Vector, Hashtable). Enumeration is the first iterator introduced in JDK 1.0. The interface Enumeration has the following methods declared in it.

Method	Description
public boolean hasMoreElements();	Tests if this enumeration contains more elements.
public Object nextElement();	Returns the next element of this enumeration.

Table 18.1: The methods defined in Enumeration interface

The Collection class defined in java.util package has its own implementation of the interface Enumeration.

Enumerations are also used to specify the input streams to a SequenceInputStream. You can create Enumeration object by calling elements() method of Vector class on any Vector object. For example, if v denotes an object of the class Vector class, then e is an object of type Enumeration referring to v is:

Enumeration e = v.elements();

Example 18.1.

The following example, illustrates the Enumeration Java cursors to traverse a collection of type Vector.

// Java program to demonstrate Enumeration

import java.util.Enumeration;

import java.util.Vector;

public class EnumerationTest {

public static void main(String[] args) {

// Create a vector and print its contents

Vector v = new Vector();

for (int i = 0; i < 10; i++)

v.addElement(i);

System.out.println(v);

// Declare an enumerator to the collection v

Enumeration e = v.elements(); // At the beginning e points to

// index just before the first element in v

while (e.hasMoreElements()) {// Enumerate each element one-by-one

int i = (Integer)e.nextElement(); //Moving cursor to next element

System.out.print(i + " "); // Print the current element

}

Java Enumeration limitations

· It is applicable to only Collection of legacy classes, like Vector and HashTable.

· Compare to other Cursors, it has very lengthy method names: hasMoreElements() and nextElement().

· In CRUD pperations, it supports only read operation. It does not support creagte, update and delete operations.

· It supports only forward direction iteration. That’s why it is also known as uni-directional cursor.

We will discuss about Iterator with some suitable examples in this post.

Iterator interface

The limitations in Enumeration interface had been addressed in JDK 1.2, and introduced a better Java cursor called Iterator. It is a universal iterator as you can apply it to any Collection object like Set, List, Queue, Deque and also in all implemented classes of Map interface. By using Iterator, you can perform both read and remove operations. The Ierator interface defines three methods as listed in Table 2. The Iterator interface is fully implemented by Collection classes.

Method	Description
public boolean hasNext();	Returns true if the iterator has more elements.
public Object next();	Returns the next element in the iterator.
public void remove();	Remove the next element in the iterator. This method can be called only once per call to next().

Table 18.2: The methods defined in Iterator interface

Example 18.2.

The following program shows an example of Iterator obeject with ArrayList class.

import java.util.*;

public class IteratorDemo {

public static void main(String[] args) {

ArrayList<Integer> al = new ArrayList<Integer>();

for (int i = 0; i < 10; i++)

al.add(i);

System.out.println(al);

Iterator itr = al.iterator();

// The cursor at the beginning of the first element

while (itr.hasNext()) { // Iterate over each element in al

int i = itr.next(); // Read the current element

System.out.print(i + " ");

if (i % 2 != 0)

itr.remove(); // Removing odd elements

}

System.out.println();

System.out.println(al);

}

Example 18.3.

Be careful. You cannot add or remove elements to the collection while using iterator over it. Following example, will give a run-time exception.

import java.util.*;

public class ErrorWithIterator {

public static void main(String args[]){

ArrayList<String> books = new ArrayList<String>();

books.add("C");

books.add("C++");

books.add("Java”);

for(String obj : books) {

System.out.println(obj);

//We are adding element while iterating list

books.add("C++");

}

Iterator itr = books.iterator();

while (itr.hasNext()) {

String b = itr.next();

System.out.print(b + " ");

books.add("Python"); // You cannot do it!

books.remove(“C”), // You cannot do it!!

}

Java Iterator limitations

· It supports only forward direction iteration. That is, like Enumerator, it is also a uni-directional cursor.

· Only read and remove is possible. Replacement and addition of new element is not supported by Iterator

ListIterator interface

It is only applicable for List collection implemented classes like arraylist, linkedList, etc. It provides bi-directional iteration. This cursor has more functionality than iterator. ListIterator interface extends Iterator interface. So all three methods of Iterator interface are available for ListIterator. In addition, there are six more methods, which are listed in Table 3.

Method	Description
void add(E obj)	Inserts obj into the list in front of the element that will be returned by the next call to next( ).
default void forEachRemaining( Consumer<? super E> action)	The action specified by action is executed on each unprocessed element in the collection. (Added by JDK 8.)
boolean hasNext( )	Returns true if there is a next element. Otherwise, returns false.
boolean hasPrevious( )	Returns true if there is a previous element. Otherwise, returns false.
E next( )	Returns the next element. A NoSuchElementException is thrown if there is not a next element.
int nextIndex( )	Returns the index of the next element. If there is not a next element, returns the size of the list.
E previous( )	Returns the previous element. A NoSuchElementException is thrown if there is not a previous element.
int previousIndex( )	Returns the index of the previous element. If there is not a previous element, returns –1.
void remove( )	Removes the current element from the list. An IllegalStateException is thrown if remove( ) is called before next( ) or previous( ) is invoked.
void set(E obj)	Assigns obj to the current element. This is the element last returned by a call to either next( ) or previous( ).

Table 18.3: The methods defined in ListIterator interface

Example 18.4.

The following program shows an example of ListIterator with ArrayList class.

import java.util.*;

class ListIteratorDemo {

public static void main(String args[]) {

// Create an array list.

ArrayList<String> al = new ArrayList<String>();

// Add elements to the array list.

al.add("C");

al.add("A");

al.add("E");

al.add("B");

al.add("D");

al.add("F");

// Use iterator to display contents of al.

System.out.print("Original contents of al: ");

Iterator<String> itr = al.iterator();

while(itr.hasNext()) {

String element = itr.next();

System.out.print(element + " ");

}

System.out.println();

// Modify objects being iterated.

ListIterator<String> litr = al.listIterator();

while(litr.hasNext()) {

String element = litr.next();

litr.set(element + "+");

}

System.out.print("Modified contents of al: ");

// Now, display the list backwards.

System.out.print("Modified list backwards: ");

while(litr.hasPrevious()) {

String element = litr.previous();

System.out.print(element + " ");

}

System.out.println();

}

Note:

If you won’t be modifying the contents of a collection or obtaining elements in reverse order, then the for-each version of the for loop is often a more convenient alternative to cycling through a collection than is using an iterator. Recall that the for can cycle through any collection of objects that implement the Iterable interface. Because all of the collection classes implement this interface, they can all be operated upon by the for.

Example 18.5.

The following example uses the for-each for loop to cycle through a collection.

import java.util.*;

class ForEachLoopDemo {

public static void main(String args[]) {

// Create an array list for integers.

ArrayList<Integer> vals = new ArrayList<Integer>();

// Add values to the array list.

vals.add(1);

vals.add(2);

vals.add(3);

vals.add(4);

vals.add(5);

// Use for loop to display the values.

System.out.print("Contents of vals: ");

for(int v : vals)

System.out.print(v + " ");

System.out.println();

// Now, sum the values by using a for loop.

int sum = 0;

for(int v : vals)

sum += v;

System.out.println("Sum of values: " + sum);

}

Note:

· Clearly the three methods that ListIterator inherits from Iterator (hasNext(), next(), and remove()) do exactly the same thing in both interfaces. The hasPrevious() and the previous operations are exact analogues of hasNext() and next(). The former operations refer to the element before the (implicit) cursor, whereas the latter refer to the element after the cursor. The previous operation moves the cursor backward, whereas next moves it forward.

· ListIterator has no current element; its cursor position always lies between the element that would be returned by a call to previous() and the element that would be returned by a call to next()

· Please note that initially any iterator reference will point to the index just before the index of first element in a collection.

· We don’t create objects of Enumeration, Iterator, ListIterator because they are interfaces. We use methods like elements(), iterator(), listIterator() to create objects. These methods have anonymous Inner classes that extends respective interfaces and return this class object. This can be verified by below code. For more on inner class refer

Example 18.6.

The following Java program demonstrates iterators references of different types to the same collection.

import java.util.Enumeration;

import java.util.Iterator;

import java.util.ListIterator;

import java.util.Vector;

public class JavaCurorsTest {

public static void main(String[] args) {

Vector v = new Vector();

// Create three iterators

Enumeration e = v.elements();

Iterator itr = v.iterator();

ListIterator ltr = v.listIterator();

// Code to use the iterators

}

Limitations of ListIterator

It is the most powerful iterator but it is only applicable for List implemented classes, so it is not a universal iterator.

Example 18.7.

This program illustrates the application of iterator with a collection of generic data type. Here, we have considered Employee class for example. Further, you note how you can customize the iterator interface with your own.

public class Employee {

private int empid;

private String ename;

private String designation;

private double salary;

public Employee(int empid,String ename,String designation,double salary){

this.empid = empid;

this.ename = ename;

this.designation = designation;

this.salary = salary;

}

public int getEmpid() {

return empid;

}

public String getEname() {

return ename;

}

public String getDesignation() {

return designation;

}

public double getSalary() {

return salary;

}

//This shows how to print an element of custom type using toString()

@Override

public String toString(){

return empid + "\t" + ename + "\t" + designation + "\t" + salary;

}

This follows the definition of main class.

import java.util.*;

public class Employees implements Iterable{

private List<Employee> emps = null;

public Employees(){

emps = new ArrayList<&glt;();

emps.add(new Employee(101,"Ram","Professor", 250000L));

emps.add(new Employee(102,"Rahim","Engineer", 300000L));

emps.add(new Employee(1003,"Jonny","Doctor", 350000L));

}

@Override

public Iterator<Employee> iterator() {

return emps.iterator();

}

public class EmployeesTester {

public static void main(String[] args) {

Employees emps = new Employees();

for(Employee emp : emps){

System.out.println(emp);

}

Splitearotr Interface

Spliterator, like other Java cursors, is for traversing the elements of a collection. Unlike other cursors, it can travesre both in parallel as well as sequential manner. The name is so because it is actually splitting + iterator to accomplish a parallel traversing. It was included in JDK 8 and is defined by the Spliterator interface. Compare to other cursors, it offers substantially more functionality. Perhaps the most important aspect of Spliterator is its ability to provide support for parallel iteration of portions of the sequence and hence providing parallel programming.

The Spliterator defines 8 methods which are listed in Table 4. All methods are duly implemented in Collection classes.

Method	Description
int characteristics( )	Returns the characteristics of the invoking spliterator, encoded into an integer.
long estimateSize( )	Estimates the number of elements left to iterate and returns the result. Returns Long.MAX_VALUE if the count cannot be obtained for any reason.
default void forEachRemaining( Consumer<? super T> action)	Applies action to each unprocessed element in the data source.
default Comparator<? super T> getComparator( )	Returns the comparator used by the invoking spliterator or null if natural ordering is used. If the sequence is unordered, IllegalStateException is thrown.
default long getExactSizeIfKnown( )	If the invoking spliterator is sized, returns the number of elements left to iterate. Returns –1 otherwise.
default boolean hasCharacteristics(int val)	Returns true if the invoking spliterator has the characteristics passed in val. Returns false otherwise.
boolean tryAdvance( Consumer<? super T> action)	Executes action on the next element in the iteration. Returns true if there is a next element. Returns false if no elements remain.
Spliterator<T> trySplit( )	If possible, splits the invoking spliterator, returning a reference to a new spliterator for the partition. Otherwise, returns null. Thus, if successful, the original spliterator iterates over one portion of the sequence and the returned spliterator iterates over the other portion.

Table 18.4: The methods defined in Spliteraor

Example 18.8:

The following program provides a simple example of Spliterator. Notice that the program demonstrates both tryAdvance( ) and forEachRemaining( ). Also notice how these methods combine the actions of Iterator’s next( ) and hasNext( ) methods into a single call.

import java.util.*;

class SpliteratorDemo {

public static void main(String args[]) {

// Create an array list for doubles.

ArrayList<Double> vals = new ArrayList<>();

// Add values to the array list.

vals.add(1.0);

vals.add(2.0);

vals.add(3.0);

vals.add(4.0);

vals.add(5.0);

// Use tryAdvance() to display contents of vals.

System.out.println("Contents of vals: ");

Spliterator<Double> spltitr = vals.spliterator();

while(spltitr.tryAdvance((n)-> System.out.println(n)));

System.out.println();

// Create new list that contains square roots.

spltitr = vals.spliterator();

ArrayList<Double> sqrs = new ArrayList<>();

while(spltitr.tryAdvance((n) -> sqrs.add(Math.sqrt(n))));

// Use forEachRemaining() to display contents of sqrs.

System.out.print("Contents of sqrs:\n");

spltitr = sqrs.spliterator();

spltitr.forEachRemaining((n) -> System.out.println(n));

System.out.println();

}

Example 18.9.

Another example is given below demonstrating the utility of other methods methods of Spliterator.

import java.util.*;

public class SpliteratorDemo {

public static void main(String[] args) {

// Create an array list for doubles.

ArrayList<Integer> al = new ArrayList<>();

// Add values to the array list.

al.add(1);

al.add(2);

al.add(-3);

al.add(-4);

al.add(5);

// Obtain a Stream to the array list.

Stream<Integer> str = al.stream();

// getting Spliterator object on al

Spliterator<Integer> splitr1 = str.spliterator();

// estimateSize method

System.out.println("estimate size : " + splitr1.estimateSize());

// getExactSizeIfKnown method

System.out.println("exact size : " + splitr1.getExactSizeIfKnown());

// hasCharacteristics and characteristics method

System.out.println(splitr1.hasCharacteristics(splitr1.characteristics()));

System.out.println("Content of arraylist :");

// forEachRemaining method

splitr1.forEachRemaining((n) -> System.out.println(n));

// Obtaining another Stream to the array list.

Stream<Integer> str1 = al.stream();

splitr1 = str1.spliterator();

// trySplit() method

Spliterator<Integer> splitr2 = splitr1.trySplit();

// If splitr1 could be split, use splitr2 first.

if(splitr2 != null) {

System.out.println("Output from splitr2: ");

splitr2.forEachRemaining((n) -> System.out.println(n));

}

// Now, use the splitr

System.out.println("\nOutput from splitr1: ");

splitr1.forEachRemaining((n) -> System.out.println(n));

}

Have a look at tryAdvance() method.It performs an action on the next element and then advances the iterator. It is shown here:

boolean tryAdvance(Consumer<? super T> action)

Here, action specifies the action that is executed on the next element in the iteration and Consumer is a functional interface that applies an action to an object. It is a generic functional interface declared in java.util.function. It has only one abstract method, accept( ), which is

shown here:

void accept(T objRef)

here T is type of object reference.

For implementing our action, we must implement accept method.To implement accept method, here we use lambda expression .This will be more clear from below example.

How to use Spliterator with Collections: Using Spliterator for basic iteration tasks is quite easy, simply call tryAdvance( ) until it returns false.

Example 18.10.

Java program to demonstrate simple Spliterator using tryAdvance method

import java.util.ArrayList;

import java.util.Spliterator;

public class SpliteratorDemo

{

public static void main(String[] args)

{

// Create an array list for doubles.

ArrayList<Integer> al1 = new ArrayList<>();

// Add values to the array list.

al1.add(1);

al1.add(2);

al1.add(-3);

al1.add(-4);

al1.add(5);

// Use tryAdvance() to display(action) contents of arraylist.

System.out.print("Contents of arraylist:\n");

// getting Spliterator object on al1

Spliterator<Integer> splitr = al1.spliterator();

// Use tryAdvance() to display(action) contents of arraylist.

// Notice how lambda expression is used to implement accept method

// of Consumer interface

while(splitr.tryAdvance((n) -> System.out.println(n)));

// Use tryAdvance() for getting absolute values(action) of contents of arraylist.

// Create new list that contains absolute values.

ArrayList<Integer> al2 = new ArrayList<>();

splitr = al1.spliterator();

// Here our action is to get absolute values

// Notice how lambda expression is used to implement accept method

// of Consumer interface

while(splitr.tryAdvance((n) -> al2.add(Math.abs(n))));

System.out.print("Absolute values of contents of arraylist:\n");

// getting Spliterator object on al2

splitr = al2.spliterator();

while(splitr.tryAdvance((n) -> System.out.println(n)));

}

Notice how tryAdvance( ) consolidates the purposes of hasNext( ) and next( ) provided by Iterator into a single method in above example. This improves the efficiency of the iteration process.

In some cases, you might want to perform some action on each element collectively, rather than one at a time. To handle this type of situation, Spliterator provides the forEachRemaining( ) method, it is generally used in cases involving streams. This method applies action to each unprocessed element and then returns.

CANADA	JAPAN	FRANCE	PRIVATE_USE_EXTENSION
CANADA_FRENCH	JAPANESE	FRENCH	ROOT
CHINA	KOREA	GERMAN	SIMPLIFIED_CHINESE
CHINESE	KOREAN	GERMANY	TAIWAN
ENGLISH	PRC	ITALIAN	TRADITIONAL_CHINESE
UNICODE_LOCALE_EXTENSION	US	ITALY	UK