ConcurrentHashMap putAll() method in Java

The java.util.concurrent.ConcurrentHashMap.putAll() is an in-built function in Java which is used for the copy operation. The method copies all of the elements i.e., the mappings, from one ConcurrentHashMap into another.

Syntax:

new_conn_hash_map.putAll(conn_hash_map)

Parameters: The function accepts a ConcurrentHashMap conn_hash_map as its only parameter and copies all its mappings with this map.

Return Value: The method does not return any values.

Exception: The function throws NullPointerException when the specified parameter is null.

Below programs illustrate the ConcurrentHashMap.putAll() method :

Program 1: This program involves mapping String Values to Integer Keys.

// Java Program Demonstrate putAll()
// method of ConcurrentHashMap

import java.util.concurrent.*;

class ConcurrentHashMapDemo {
    public static void main(String[] args)
    {
        ConcurrentHashMap<Integer, String> chm =
                           new ConcurrentHashMap<Integer, String>();
        chm.put(100, "Geeks");
        chm.put(101, "for");
        chm.put(102, "Geeks");
        chm.put(103, "Gfg");
        chm.put(104, "GFG");

        // Displaying the existing HashMap
        System.out.println("Initial Mappings are: "
                           + chm);

        ConcurrentHashMap<Integer, String> new_chm =
                            new ConcurrentHashMap<Integer, String>();
        new_chm.putAll(chm);

        // Displaying the new map
        System.out.println("New mappings are: "
                           + new_chm);
    }
}

Output:

Initial Mappings are: {100=Geeks, 101=for, 102=Geeks, 103=Gfg, 104=GFG}
New mappings are: {100=Geeks, 101=for, 102=Geeks, 103=Gfg, 104=GFG}

Program 2: This program involves mapping Integer Values to String Keys.

// Java Program Demonstrate putAll()
// method of ConcurrentHashMap

import java.util.concurrent.*;

class ConcurrentHashMapDemo {
    public static void main(String[] args)
    {
        ConcurrentHashMap<String, Integer> chm =
                   new ConcurrentHashMap<String, Integer>();
        chm.put("Gfg", 100);
        chm.put("GFG", 102);
        chm.put("GfG", 18);
        chm.put("gfg", 15);
        chm.put("gfG", 55);

        // Displaying the existing HashMap
        System.out.println("Initial Mappings are: "
                           + chm);

        ConcurrentHashMap<String, Integer> new_chm =
                  new ConcurrentHashMap<String, Integer>();

        // Copying the contents
        new_chm.putAll(chm);

        // Inserting a new mapping
        new_chm.put("gFg", 22);
        // Displaying the new map
        System.out.println("New mappings are: "
                           + new_chm);
    }
}

Output:

Initial Mappings are: {Gfg=100, GFG=102, GfG=18, gfg=15, gfG=55}
New mappings are: {Gfg=100, GFG=102, GfG=18, gfg=15, gfG=55, gFg=22}

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ConcurrentHashMap.html#putAll()