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Java HashMap putAll() Method with Example

HashMap Class putAll() method: Here, we are going to learn about the putAll() method of HashMap Class with its syntax and example.
Submitted by Preeti Jain, on March 04, 2020

HashMap Class putAll() method

• putAll() method is available in java.util package.
• putAll() method is used to copy all of the key-value pairs that exist from the given map and paste it to this HashMap.
• 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 copying mappings.
  NullPointerException: This exception may throw when the given parameter is null exists.

Syntax:

    public void putAll(Map m);

Parameter(s):

• Map m – represents the map that contains mappings to be copied.

Return value:

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

Example:

// Java program to demonstrate the example 
// of void putAll(Map m) method of HashMap 

import java.util.*;

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

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

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

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

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

Output

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