Module# 15: Java and Utilities Lecture#60: Java Cursors

// Example 60.1 : Demonstration of enumeration

// 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 at the beginning e points to

index just before the first element in v */

Enumeration e = v.elements();

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

}

}

}

// Example 60.2 : Iterator object 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 60.3 : Add or remove while using Iterator

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);

books.add("C#"); // We are adding element while iterating list

}

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!!

}

}

}

// Example 60.4 : ListIterator with ArrayList collection

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();

}

}

// Example 60.5 : Cycle through a collection using for-each

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);

}

}

// Example 60.6 : 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

}

}

// Example 60.7 : Iterators references of different types to the same collection

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;

}

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

@Override

public String toString(){

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

}

}

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);

}

}

}

// Example 60.8 : Spliterator illustration

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 60.9 : Utility of other 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));

}

}

// Example 60.10 : 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)));

}

}