void putAll(Map<? extends K, ? extends V> map);

package in.bench.resources.java.map;

import java.util.HashMap;

public class AddOneHashMapToAnotherHashMap {

	public static void main(String[] args) {

		// creating HashMap object of type <String, String>
		HashMap<String, String> hashMap1 = new HashMap<String, String>(); 

		// adding key-value pairs to 1st HashMap object
		hashMap1.put("Google", "Sundar Pichai");
		hashMap1.put("Apple", "Steve Jobs");
		hashMap1.put("Amazon", "Jeff Bezos");

		// Original HashMap-1 contents
		System.out.println("Original HashMap-1 contents: \n"
				+ hashMap1);

		// creating HashMap object of type <String, String>
		HashMap<String, String> hashMap2 = new HashMap<String, String>(); 

		// adding key-value pairs to 2nd HashMap object
		hashMap2.put("Microsoft", "Bill Gates");
		hashMap2.put("Whatsup", "Brian Acton");

		// HashMap-2 contents
		System.out.println("\n\nHashMap-2 contents: \n"
				+ hashMap2);

		// put all hashMap2 contents into original hashMap1
		hashMap1.putAll(hashMap2);

		// Modified HashMap-1 contents
		System.out.println("\n\nModified HashMap-1 contents: \n"
				+ hashMap1);
	}
}

Original HashMap-1 contents:
{Google=Sundar Pichai, Apple=Steve Jobs, Amazon=Jeff Bezos}

HashMap-2 contents:
{Microsoft=Bill Gates, Whatsup=Brian Acton}

Modified HashMap-1 contents:
{Google=Sundar Pichai, Microsoft=Bill Gates, Apple=Steve Jobs,
Amazon=Jeff Bezos, Whatsup=Brian Acton}