Module# 09: Table and Map Lecture#38: Applications of Map Part-I

// Example 38.1: Creating a Map

/* This example creates a map container and add objects into it using the put() method. */

import java.util.*;

class HashMapCreateDemo {

public static void main(String args[]) {

// Create a hash map object as a container.

HashMap<Double, String>hMap = new HashMap<Double, String>();

// Put elements to the map container

hMap.put(200.0, "OK");

hMap.put(303.0, "See Other");

hMap.put(404.0, "Not Found");

hMap.put(500.0, "Internal Server Error");

System.out.println(hMap); // Printing the container

}

}

// Example 38.2: Adding object with duplicate values

/* This example creates a map container using the put() method and with duplicate entries. */

import java.util.*;

class HashMapDuplicateDemo {

public static void main(String args[]) {

// Create a hash map object as a container.

HashMap<Integer, String>hMap = new HashMap<Integer, String>();

// Put elements to the map container with duplicates

hMap.put(200, "OK");

hMap.put(303, "See Other");

hMap.put(404, "Not Found");

hMap.put(500, "Internal Server Error");

hMap.put(303, "Invalid entry");

hMap.put(101, "See Other");

System.out.println(hMap); // Printing the container

}

}

// Example 38.3: Copying a Map into other

/* This example creates a map container that copies elements from an existing map. */

import java.util.*;

class HashMapCopyDemo {

public static void main(String args[]) {

// Create a hash map object as a container.

Map<String, Double> hMap1 = new HashMap<>();

// Put elements to the map container

hMap1.put("John Doe", new Double(3434.34));

hMap1.put("Tom Smith", new Double(123.22));

hMap1.put("Jane Baker", new Double(1378.00));

hMap1.put("Tod Hall", new Double(99.22));

hMap1.put("Ralph Smith", new Double(-19.08));

System.out.println(hMap1); // Printing the container

// Create a copy of a hMap1 to hMap2

Map<String,Double> hMap2 = new HashMap<>(hMap1);

// Add data into hMap2

hMap1.put("Robin Keith", new Double(423.22));

hMap2.put("Peter Hwang", new Double(178.00));

System.out.println(hMap2); // Printing the container

}

}

// Example 38.4: Retrieving objects from a Map container

/* This example illustrates how an object stored in a map framework can be accessed using get(). */

import java.util.*;

class HashMapAcsessDemo {

public static void main(String args[]) {

// Create a hash map object as a container.

Map<String, Double>hMap = new HashMap<>();

// Put elements to the map container

hMap.put("John Doe", new Double(3434.34));

hMap.put("Tom Smith", new Double(123.22));

hMap.put("Jane Baker", new Double(1378.00));

hMap.put("Tod Hall", new Double(99.22));

hMap.put("Ralph Smith", new Double(-19.08));

// Deposit 1000 into John Doe's account.

double balance = hMap.get("John Doe");

hMap.put("John Doe", balance + 1000);

System.out.println("John Doe's current balance: " + hMap.get("John Doe"));

}

}

// Example 38.5: Removing objects from a Map container

/* There are two methods, namely remove() and replace() that you can use for remove an entry in a map framework. The following example illustrates how an object stored in a map framework can be removed. */

import java.util.*;

class HashMapRemoveDemo {

public static void main(String args[]) {

// Create a hash map object as a container.

Map<String, Double>hMap = new HashMap<>();

// Put elements to the map container

hMap.put("John Doe", new Double(3434.34));

hMap.put("Tom Smith", new Double(123.22));

hMap.put("Jane Baker", new Double(1378.00));

hMap.put("Tod Hall", new Double(99.22));

hMap.put("Ralph Smith", new Double(-19.08));

Double val = hMap.remove("Jane Baker");

if (val != null) {System.out.println("Removed value: " + val);}

System.out.println(hMap);

hMap.remove("Tod Hall", 99.22);

System.out.println(hMap);

hMap.replace("Ralph Smith", 545.67);

System.out.println(hMap);

}

}

// Example 38.6: Retrieving objects from a Map container

/* The following example illustrates how an object stored in a map framework can be accessed. For this, you should use the get(). */

import java.util.*;

class HashMapAcsessDemo {

public static void main(String args[]) {

// Create a hash map object as a container.

Map<String, Double>hMap = new HashMap<>();

// Put elements to the map container

hMap.put("John Doe", new Double(3434.34));

hMap.put("Tom Smith", new Double(123.22));

hMap.put("Jane Baker", new Double(1378.00));

hMap.put("Tod Hall", new Double(99.22));

hMap.put("Ralph Smith", new Double(-19.08));

// Deposit 1000 into John Doe's account.

double balance = hMap.get("John Doe");

hMap.put("John Doe", balance + 1000);

System.out.println("John Doe's current balance: " + hMap.get("John Doe"));

}

}

// Example 38.7: Accessing the status of a map

/* There are two methods, namely size() and isEmpty() that can be used to check the status of a map container. The following example illustrates how an object stored in a map framework can be viewed. */

class HashMapViewDemo {

public static void main(String args[]) {

// Create a hash map object as a container.

HashMap<Integer, String>hMap = new HashMap<Integer, String>();

// Put elements to the map container

hMap.put(200, "OK");

hMap.put(303, "See Other");

hMap.put(404, "Not Found");

hMap.put(500, "Internal Server Error");

// Checking the container

if (hMap.isEmpty()) {

System.out.println("Error: The container is empty");

} else {

System.out.println(hMap); // Printing the container

}

// Printing the size of the container

System.out.println("Size : " + hMap.size());

}

}

// Example 38.8: Map iteration

/* This program illustrates the above here ways f iterating over a map container */

import java.util.*;

class HashMapIterationDemo {

public static void main(String args[]) {

// Create a hash map object as a container.

Map<String, String>mapCountryCodes = new HashMap<>();

mapCountryCodes.put("1", "USA");

mapCountryCodes.put("44", "United Kingdom");

mapCountryCodes.put("33", "France");

mapCountryCodes.put("81", "Japan");

mapCountryCodes.put("91", "India");

// Collection view using keySet()

Set<String>setCodes = mapCountryCodes.keySet();

Iterator<String> iterator = setCodes.iterator();

while(iterator.hasNext()) {

String code = iterator.next();

String country = mapCountryCodes.get(code);

System.out.println(code + " => "+ country);

}

// Collection view using values()

Collection<String> countries = mapCountryCodes.values();

for(String country : countries) {

System.out.println(country);

}

// Collection view using entrySet()

Set<Map.Entry<String, String>> entries =

mapCountryCodes.entrySet();

for(Map.Entry<String, String>entry : entries) {

String code = entry.getKey();

String country = entry.getValue();

System.out.println(code + " => "+ country);

}

// Collection view using Lambda expression

mapCountryCodes.forEach((code, country) ->

System.out.println(code + " => "+ country));

}

}

// Example 38.9: Performing bulk operations with Maps

/* This program illustrates the above here ways f iterating over a map container */

import java.util.*;

class HashMapBulkOperationDemo {

public static void main(String args[]) {

// Create two map object containers.

Map<Integer, String>countryCodesEU = new HashMap<>();

countryCodesEU.put(44, "United Kingdom");

countryCodesEU.put(33, "France");

countryCodesEU.put(49, "Germany");

Map<Integer, String>countryCodesWorld = new HashMap<>();

countryCodesWorld.put(1, "United States");

countryCodesWorld.put(86, "China");

countryCodesWorld.put(82, "South Korea");

System.out.println("Before: " + countryCodesWorld);

// Merger two containers using putAll()

countryCodesWorld.putAll(countryCodesEU);

System.out.println("After: " + countryCodesWorld);

// Clear one map container

countryCodesEU.clear();

System.out.println("Is map empty? "+ countryCodesEU.isEmpty());

}

}