Map keySet() Method in Java with Examples

This method is used to return a Set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa.

Syntax:

Set keySet()

Parameters: This method has no argument.

Returns: This method returns a set containing keys of the specified map.

Below programs show the implementation of int keySet() method.

Program 1:

// Java code to show the implementation of
// isEmpty method in Map interface
import java.util.*;
public class GfG {

    // Driver code
    public static void main(String[] args)
    {

        // Initializing a Map of type HashMap
        Map<String, String> map = new HashMap<>();

        System.out.println(map);

        System.out.println(map.isEmpty());
    }
}

Output:

{}
true

Program 2: Below is the code to show implementation of hashCode().

// Java code to show the implementation of
// keySet method in Map interface
import java.util.*;
public class GfG {

    // Driver code
    public static void main(String[] args)
    {

        // Initializing a Map of type HashMap
        Map<Integer, String> map = new HashMap<>();
        Set<Integer> s = new HashSet<>();
        map.put(1, "One");
        map.put(3, "Three");
        map.put(5, "Five");
        map.put(7, "Seven");
        map.put(9, "Nine");
        System.out.println(map);
        s = map.keySet();
        System.out.println(s);
    }
}

Output:

{1=One, 3=Three, 5=Five, 7=Seven, 9=Nine}
[1, 3, 5, 7, 9]

Reference:
Oracle Docs