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Java WeakHashMap putAll() Method with Example

WeakHashMap Class putAll() method: Here, we are going to learn about the putAll() method of WeakHashMap Class with its syntax and example.
Submitted by Preeti Jain, on February 23, 2020

WeakHashMap Class putAll() method

  • putAll() method is available in java.util package.
  • putAll() method is used to copy all of the associations or mappings from the given map and assign it to this map.
  • putAll() method is a non-static method, it is accessible with the class object only and if we try to access the method with the class name then we will get an error.
  • putAll() method may throw an exception at the time of copy mappings.
    NullPointerException: This exception may throw when the given parameter is null exists.


    public void putAll(Map map);


  • Map map – represents the mappings to be saved in this map.

Return value:

The return type of the method is void, it returns nothing.


// Java program to demonstrate the example 
// of void putAll(Map map) method of WeakHashMap 

import java.util.*;

public class PutAllOfWeakHashMap {
    public static void main(String[] args) {
        // Instantiates a WeakHashMap object
        Map < Integer, String > map = new WeakHashMap < Integer, String > ();
        Map < Integer, String > put_map = new WeakHashMap < Integer, String > ();

        // By using put() method is to add
        // key-value pairs in a WeakHashMap
        map.put(10, "C");
        map.put(20, "C++");
        map.put(50, "JAVA");
        map.put(40, "PHP");
        map.put(30, "SFDC");

        // Display WeakHashMap
        System.out.println("WeakHashMap: " + map);

        // By using putAll() method is to
        // copy all of the elements of the given
        // object and paste it in an another object

        // Display put_map WeakHashMap
        System.out.print("put_map.putAll(map): " + put_map);


WeakHashMap: {30=SFDC, 40=PHP, 10=C, 20=C++, 50=JAVA}
put_map.putAll(map): {30=SFDC, 10=C, 40=PHP, 20=C++, 50=JAVA}


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