Java HashMap keySet()

The syntax of the keySet() method is:

hashmap.keySet()

Here, hashmap is an object of the HashMap class.

keySet() Parameters

The keySet() method does not take any parameter.

keySet() Return Value

• returns a set view of all the keys of the hashmap

Note: The set view only shows all keys of the hashmap as a set. The view does not contain actual keys. To learn more about view in Java, visit the view of a collection.

Example 1: Java HashMap keySet()

import java.util.HashMap;

class Main {
  public static void main(String[] args) {
    // create an HashMap
    HashMap<String, Integer> prices = new HashMap<>();

    // insert entries to the HashMap
    prices.put("Shoes", 200);
    prices.put("Bag", 300);
    prices.put("Pant", 150);
    System.out.println("HashMap: " + prices);

    // return set view of all keys
    System.out.println("Keys: " + prices.keySet());
  }
}

Output

HashMap: {Pant=150, Bag=300, Shoes=200}
Keys: [Pant, Bag, Shoes]

In the above example, we have created a hashmap named prices. Notice the expression,

prices.keySet()

Here, the keySet() method returns a set view of all the keys present in the hashmap.

The keySet() method can also be used with the for-each loop to iterate through each key of the hashmap.

Example 2: keySet() Method in for-each Loop

import java.util.HashMap;

class Main {
  public static void main(String[] args) {

    // Creating a HashMap
    HashMap<String, Integer> numbers = new HashMap<>();
    numbers.put("One", 1);
    numbers.put("Two", 2);
    numbers.put("Three", 3);
    System.out.println("HashMap: " + numbers);

    // access all keys  of the HashMap
    System.out.print("Keys: ");

    // keySet() returns a set view of all keys
    // for-each loop access each key from the view
    for(String key: numbers.keySet()) {

      // print each key
      System.out.print(key + ", ");
    }
  }
}

Output

HashMap: {One=1, Two=2, Three=3}
Keys: One, Two, Three,

In the above example, we have created a hashmap named numbers. Notice the line,

String key:  numbers.keySet()

Here, the keySet() method returns a set view of all the keys. The variable key access each key from the view.

Note: The Key of HashMap is of String type. Hence, we have used the String variable to access the keys.

Recommended Reading

• HashMap entrySet() - returns set view of all mappings (entries)
• HashMap values() - returns set view of all values