Map entrySet() method in Java with Examples

The entrySet() method of the java.util.Map interface returns a set view of all key–value mappings in the map, where each element is a Map.Entry<K, V>.

• Each Map.Entry represents a single key–value pair from the map.
• It allows simultaneous access to both keys and values during iteration.
• More efficient than keySet() when values are also required, as it avoids extra get() calls.

import java.util.*;

class GFG {
    public static void main(String[] args) {
        Map<Integer, String> map = new HashMap<>();
        map.put(1, "Java");
        map.put(2, "Python");

        for (Map.Entry<Integer, String> e : map.entrySet()) {
            System.out.println(e.getKey() + " : " + e.getValue());
        }
    }
}

1 : Java
2 : Python

Explanation:

• entrySet() returns a set view of all key–value pairs in the map.
• Each element in the set is a Map.Entry object containing a key and its corresponding value.
• This approach allows efficient iteration when both keys and values are required.

Syntax

map.entrySet()

• Parameters: The method does not take any parameter.
• Return Value: The method returns a set having same elements as the hash map. Below programs illustrate the java.util.Map.entrySet() Method:

Note: The returned set is backed by the map, meaning changes to the map are reflected in the set and vice versa.

Example: Iterating Over a Map Using entrySet()

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Map<Integer, String> map = new HashMap<>();
        map.put(1, "Java");
        map.put(2, "Python");
        map.put(3, "C++");

        for (Map.Entry<Integer, String> entry : map.entrySet()) {
            System.out.println(entry.getKey() + " = " + entry.getValue());
        }
    }
}

1 = Java
2 = Python
3 = C++

Explanation:

• entrySet() returns a set of key–value pairs.
• Each iteration gives a Map.Entry object.
• getKey() retrieves the key, and getValue() retrieves the value.

Example: Modifying Values Using entrySet()

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();
        map.put("Apple", 10);
        map.put("Banana", 5);

        for (Map.Entry<String, Integer> entry : map.entrySet()) {
            entry.setValue(entry.getValue() + 5);
        }

        System.out.println(map);
    }
}

{Apple=15, Banana=10}

Explanation:

• setValue() updates the value of the current entry.
• Since entrySet() is backed by the map, changes reflect in the original map.

entrySet() vs keySet()