Hashtable remove(Object) in Java

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

Syntax:

V java.util.Hashtable.remove(Object key)

This method takes one argument. This method removes the key (and its corresponding value) from this hashtable.

Note: This method does nothing if the key is not in the hashtable.

Parameters: One parameter is required for this method.

key: the key that needs to be removed.

Returns: the value to which the key had been mapped in this hashtable, or null if the key did not have a mapping.

Throws:

NullPointerException - if the key is null

Approach 1: When no exception

Java

import java.util.Hashtable;

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

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

        Object key = "Hello";
        hashtable.remove(key);

        System.out.println(hashtable);

    }
}

Output:

{World=2}

Approach 2: NullPointerException 

Java

import java.util.Hashtable;

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

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

        Object key = null;
        hashtable.remove(key);

        System.out.println(hashtable);

    }
}

Output:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Object.hashCode()" because "key" is null
	at java.base/java.util.Hashtable.remove(Hashtable.java:508)