Java Utility Library

Java HashMap - keySet() Method

The java.util.HashMap.keySet() method returns 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

public Set<K> keySet()

Here, K is the type of key maintained by the container.

Parameters

No parameter is required.

Return Value

Returns a set view of the keys contained in this map.

Exception

Example:

In the example below, the java.util.HashMap.keySet() method returns a set view of the keys contained in the given HashMap.

import java.util.*;

public class MyClass {
  public static void main(String[] args) {
    //creating a hash map
    HashMap<Integer, String> MyMap = new HashMap<Integer, String>();

    //populating hash map
    MyMap.put(101, "John");
    MyMap.put(102, "Marry");
    MyMap.put(103, "Kim");
    MyMap.put(104, "Jo");
    MyMap.put(105, "Sam");

    //printing the content of the HashMap
    System.out.println("MyMap contains: " + MyMap);

    //creating a set view of keys of the HashMap
    Set SetView = MyMap.keySet();

    //printing the set view of keys
    System.out.println("SetView contains: " + SetView);
  }
}

The output of the above code will be:

MyMap contains: {101=John, 102=Marry, 103=Kim, 104=Jo, 105=Sam}
SetView contains: [101, 102, 103, 104, 105]

❮ Java.util - HashMap