Java HashMap containsKey()

In Java, HashMap is a class that implements the Map interface, which represents a collection of objects that are mapped to keys. HashMap uses a hash table to store the objects and their keys.

The containsKey() method in HashMap is used to check if a particular key is present in the hash table. This method returns a boolean value of true if the specified key is present, and false otherwise.

public boolean containsKey(Object key)

Here, the key parameter is the key whose presence in the HashMap is to be tested.

Example

import java.util.HashMap;

public class HashMapDemo {
    public static void main(String[] args) {
        // Creating a HashMap
        HashMap<String, Integer> marks = new HashMap<>();

        // Adding marks of students
        marks.put("Alice", 90);
        marks.put("Bob", 85);
        marks.put("Charlie", 95);
        marks.put("Dave", 80);

        // Checking if a key is present
        boolean isPresent = marks.containsKey("Alice");
        System.out.println("Is Alice present? " + isPresent);

        // Checking if a key is absent
        isPresent = marks.containsKey("Eve");
        System.out.println("Is Eve present? " + isPresent);
    }
}

Output:

Is Alice present? true
Is Eve present? false

In the above example, a HashMap named marks is created to store the marks of various students. The containsKey() method is used to check if the key "Alice" is present in the HashMap. Since "Alice" is present, the output is true. Similarly, the presence of key "Eve" is checked, which is absent, so the output is false.