Java Tutorial

Java Control Statements

Object Oriented Programming

Java Built-in Classes

Java File Handling

Java Error & Exceptions

Java Multithreading

Java Synchronization

Java Networking

Java Collections

Java List Interface

Java Queue Interface

Java Map Interface

Java Set Interface

Java Data Structures

Java Collections Algorithms

Java Miscellaneous

Advanced Java

Java APIs & Frameworks

Java Useful Resources

Java - The Map.Entry Interface

The Map.Entry interface enables you to work with a map entry.

The entrySet( ) method declared by the Map interface returns a Set containing the map entries. Each of these set elements is a Map.Entry object.

Following table summarizes the methods declared by this interface −

Sr.No. Method & Description
1

boolean equals(Object obj)

Returns true if obj is a Map.Entry whose key and value are equal to that of the invoking object.
2

Object getKey( )

Returns the key for this map entry.
3

Object getValue( )

Returns the value for this map entry.
4

int hashCode( )

Returns the hash code for this map entry.
5

Object setValue(Object v)

Sets the value for this map entry to v. A ClassCastException is thrown if v is not the correct type for the map. A NullPointerException is thrown if v is null and the map does not permit null keys. An UnsupportedOperationException is thrown if the map cannot be changed.

Example 1

Following is an example showing how Map.Entry can be used to get values of a map entry −

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class HashMapDemo {

   public static void main(String args[]) {
      // Create a hash map
      HashMap<String, Double> hm = new HashMap<>();

      // Put elements to the map
      hm.put("Zara", Double.valueOf(3434.34));
      hm.put("Mahnaz", Double.valueOf(123.22));
      hm.put("Ayan", Double.valueOf(1378.00));
      hm.put("Daisy", Double.valueOf(99.22));
      hm.put("Qadir", Double.valueOf(-19.08));
      
      // Get a set of the entries
      Set<Map.Entry<String, Double>> set = hm.entrySet();
      
      // Get an iterator
      Iterator<Map.Entry<String, Double>> i = set.iterator();
     
      // Display elements 
      while(i.hasNext()) {
         Map.Entry<String, Double> me = i.next();
         System.out.print(me.getKey() + ": ");
         System.out.println(me.getValue());
      }
   }
}

Output

Daisy: 99.22
Ayan: 1378.0
Zara: 3434.34
Qadir: -19.08
Mahnaz: 123.22

Example 2

Following is an example showing how Map.Entry can be used to set values of a map entry −

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class HashMapDemo {

   public static void main(String args[]) {
      // Create a hash map
      HashMap<String, Double> hm = new HashMap<>();

      // Put elements to the map
      hm.put("Zara", Double.valueOf(3434.34));
      hm.put("Mahnaz", Double.valueOf(123.22));
      hm.put("Ayan", Double.valueOf(1378.00));
      hm.put("Daisy", Double.valueOf(99.22));
      hm.put("Qadir", Double.valueOf(-19.08));
      
      // Get a set of the entries
      Set<Map.Entry<String, Double>> set = hm.entrySet();
      
      // Get an iterator
      Iterator<Map.Entry<String, Double>> i = set.iterator();
     
      // Display elements 
      while(i.hasNext()) {
         Map.Entry<String, Double> me = i.next();
         me.setValue(me.getValue() * 10);
         System.out.print(me.getKey() + ": ");
         System.out.println(me.getValue());
      }
   }
}

Output

Daisy: 992.2
Ayan: 13780.0
Zara: 34343.4
Qadir: -190.79999999999998
Mahnaz: 1232.2

Example 3

Following is an example showing how Map.Entry can be used to get key of a map entry −

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class HashMapDemo {

   public static void main(String args[]) {
      // Create a hash map
      HashMap<String, Double> hm = new HashMap<>();

      // Put elements to the map
      hm.put("Zara", Double.valueOf(3434.34));
      hm.put("Mahnaz", Double.valueOf(123.22));
      hm.put("Ayan", Double.valueOf(1378.00));
      hm.put("Daisy", Double.valueOf(99.22));
      hm.put("Qadir", Double.valueOf(-19.08));
      
      // Get a set of the entries
      Set<Map.Entry<String, Double>> set = hm.entrySet();
      
      // Get an iterator
      Iterator<Map.Entry<String, Double>> i = set.iterator();
     
      // Display elements 
      while(i.hasNext()) {
         Map.Entry<String, Double> me = i.next();
         System.out.println(me.getKey());
      }
   }
}

Output

Daisy
Ayan
Zara
Qadir
Mahnaz
java_collections.htm
Advertisements