IdentityHashMap replace(K, V) in Java

replace(K, V): This method is available in java.util.IdentityHashMap class of Java.

Syntax:

V java.util.Map.replace(K key, V value)

This method takes two arguments. This method replaces the entry for the specified key only if it is currently mapped to some value.

Parameters: Two parameters are required for this method.

key: key with which the specified value is associated.

value: value to be associated with the specified key.

Returns: the previous value associated with the specified key, or null if there was no mapping for the key.

Throws:

1. UnsupportedOperationException - if the put operation is not supported by this map.

2. ClassCastException - if the class of the specified key or value prevents it from being stored in this map.

3. NullPointerException - if the specified key or value is null, and this map does not permit null keys or values.

4. IllegalArgumentException - if some property of the specified key or value prevents it from being stored in this map.

Approach

Java

import java.util.IdentityHashMap;

public class IdentityHashMapreplace {

    public static void main(String args[]) {

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

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

        String key = "Hello";
        Integer value = 45;
        System.out.println(identityHashMap.replace(key, value));

    }

}

Output:

2