IdentityHashMap putAll(Map) in Java

putAll(Map): This method is available in java.util.IdentityHashMap class of Java.

Syntax:

void java.util.IdentityHashMap.putAll(Map<? extends K, ? extends V> m).

This method copies all of the mappings from the specified map to this map. These mappings will replace any mappings that this map had for any of the keys currently in the specified map.

Parameters: One parameter is required for this method.

m: mappings to be stored in this map.

Returns: NA

Throws:

NullPointerException - if the specified map is null

Approach 1: When no exception

Java

import java.util.IdentityHashMap;

public class IdentityHashMapputAll {

    public static void main(String args[]) {

        IdentityHashMap<String, Integer> identityHashMap = 
                    new IdentityHashMap<String, Integer>();

        identityHashMap.put("Java", 1);
        identityHashMap.put("Hello", 2);

        IdentityHashMap<String, Integer> identityHashMap2 = 
                    new IdentityHashMap<String, Integer>();

        identityHashMap2.putAll(identityHashMap);

        System.out.println(identityHashMap2);

    }

}

Output:

{Java=1, Hello=2}

Approach 2: NullPointerException

Java

import java.util.IdentityHashMap;

public class IdentityHashMapputAll {

    public static void main(String args[]) {

        IdentityHashMap<String, Integer> identityHashMap = null;

        IdentityHashMap<String, Integer> identityHashMap2 = 
                      new IdentityHashMap<String, Integer>();

        identityHashMap2.putAll(identityHashMap);

        System.out.println(identityHashMap2);

    }

}

Output:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.util.Map.size()" because "m" is null
	at java.base/java.util.IdentityHashMap.putAll(IdentityHashMap.java:502)