WeakHashMap putIfAbsent(K, V) in Java

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

Syntax:

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

This method takes two arguments. If the specified key is not already associated with a value associated with the given value and returns null, else returns the current value.

Parameters: Two parameters are required for this method.

key: key with which the specified value is to be 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 key or value is of an inappropriate type for 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.WeakHashMap;

public class WeakHashMapputIfAbsent {
    public static void main(String[] args) {

        WeakHashMap<String, Integer> weakHashMap = 
                   new WeakHashMap<String, Integer>();

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

        String key = "C++";
        Integer value = 3;

        System.out.println(weakHashMap.putIfAbsent(key, value));

    }
}

Output:

null