Hashtable containsKey(Object) in Java

containsKey(Object): This method is available in java.util.Hashtable class of Java.

Syntax:

boolean java.util.Hashtable.containsKey(Object key)

This method takes one argument. This method tests if the specified object is a key in this hashtable.

Parameters: One parameter is required for this method.

key: possible key.

Returns: true if and only if the specified object is a key in this hashtable, as determined by the equals method; false otherwise.

Throws:

NullPointerException - if the key is null.

Approach 1: When no exception

Java

import java.util.Hashtable;

public class HashtablecontainsKey {
    public static void main(String[] args) {
        Hashtable<String, Integer> hashtable =
                      new Hashtable<String, Integer>();

        hashtable.put("Hello", 1);
        hashtable.put("World", 2);

        String key = "Hello";

        System.out.println(hashtable.containsKey(key));

    }
}

Output:

true

Approach 2: NullPointerException 

Java

import java.util.Hashtable;

public class HashtablecontainsKey {
    public static void main(String[] args) {
        Hashtable<String, Integer> hashtable = 
                        new Hashtable<String, Integer>();

        hashtable.put("Hello", 1);
        hashtable.put("World", 2);

        String key = null;

        System.out.println(hashtable.containsKey(key));

    }
}

Output:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Object.hashCode()" because "key" is null
	at java.base/java.util.Hashtable.containsKey(Hashtable.java:353)