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

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