Map putAll() Method in Java with Examples

This method is used to copy all of the mappings from the specified map to this map.

Syntax:

void putAll(Map m)

Parameters: This method has the only argument map m, which contains key-value mappings to be copied to given map.

Returns: This method returns previous value associated with the key if present, else return -1.

Below programs show the implementation of int putAll() method.

Program 1:

// Java code to show the implementation of
// putAll method in Map interface

import java.util.*;
public class GfG {

    // Driver code
    public static void main(String[] args)
    {

        // Initializing a Map of type HashMap
        Map<Integer, String> map = new HashMap<>();
        map.put(1, "One");
        map.put(3, "Three");
        map.put(5, "Five");
        map.put(7, "Seven");
        map.put(9, "Nine");
        System.out.println(map);

        Map<Integer, String> mp = new HashMap<>();
        mp.put(10, "Ten");
        mp.put(30, "Thirty");
        mp.put(50, "Fifty");

        map.putAll(mp);

        System.out.println(map);
    }
}

Output:

{1=One, 3=Three, 5=Five, 7=Seven, 9=Nine}
{1=One, 50=Fifty, 3=Three, 5=Five, 7=Seven, 9=Nine, 10=Ten, 30=Thirty}

Program 2: Below is the code to show implementation of put().

// Java code to show the implementation of
// putAll method in Map interface
import java.util.*;
public class GfG {

    // Driver code
    public static void main(String[] args)
    {

        // Initializing a Map of type HashMap
        Map<String, String> map = new HashMap<>();
        map.put("1", "One");
        map.put("3", "Three");
        map.put("5", "Five");
        map.put("7", "Seven");
        map.put("9", "Nine");
        System.out.println(map);

        Map<String, String> mp = new HashMap<>();
        mp.put("10", "Ten");
        mp.put("30", "Thirty");
        mp.put("50", "Fifty");

        map.putAll(mp);

        System.out.println(map);
    }
}

Output:

{1=One, 3=Three, 5=Five, 7=Seven, 9=Nine}
{1=One, 3=Three, 5=Five, 7=Seven, 9=Nine, 50=Fifty, 30=Thirty, 10=Ten}

Reference:
Oracle Docs