.containsKey()

The .containsKey() method is declared in the Map interface and is implemented in the HashMap class. It is used to determine if a Map object contains a specific key. The function returns a boolean value true if the key exists, and false if not.

Syntax

The .containsKey() method can be called on a HashMap instance and it requires one parameter, the key that needs to be checked:

hashMap.containsKey(key);

• key: This can take on the form of any type of Object.

Example

In the example below, the .containsKey() method is used to check for the presence of the keys Apples and Bananas within a HashMap:

import java.util.HashMap;

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

    // creating a new HashMap which maps string keys to integer values
    HashMap<String, Integer> basket = new HashMap<String, Integer>();

    // adding fruits to the basket
    basket.put("Apples", 50);
    basket.put("Oranges", 30);

    // check if "Apples" is a key
    System.out.println("Basket contains Apples: " + basket.containsKey("Apples"));

    // check if "Bananas is a key
    System.out.println("Basket contains Bananas: " + basket.containsKey("Bananas"));
  }
}

The above example will give the following output:

Basket contains Apples: true
Basket contains Bananas: false