Java HashMap putAll() Method

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Description

The Java HashMap putAll(Map<? extends K,? extends V> m) method is used to copy all of the mappings from the specified map to this map.

Declaration

Following is the declaration for java.util.HashMap.putAll() method.

 public void putAll(Map<? extends K,? extends V> m) 

Parameters

m − This is the mappings to be stored in this map.

Return Value

NA

Exception

NullPointerException − This is thrown if the specified map is null.

Adding multiple key,value pairs in a HashMap of Integer, Integer Pair Example

The following example shows the usage of Java HashMap putAll() method to put few values in a Map. We've created a Map object of Integer,Integer pair. Then few entries are added using put() method and then map is printed. A new map is populated using putAll() method and then printed.

 package com.tutorialspoint; import java.util.HashMap; public class HashMapDemo { public static void main(String args[]) { // create hash map HashMap<Integer,Integer> newmap = new HashMap<>(); HashMap<Integer,Integer> newmap2 = new HashMap<>(); // populate hash map newmap.put(1, 1); newmap.put(2, 2); newmap.put(3, 3); System.out.println("Map elements: " + newmap); newmap2.putAll(newmap); System.out.println("Map elements: " + newmap2); } } 

Output

Let us compile and run the above program, this will produce the following result.

 Map elements: {1=1, 2=2, 3=3} Map elements: {1=1, 2=2, 3=3} 

Adding multiple key,value pairs in a HashMap of Integer, String Pair Example

The following example shows the usage of Java HashMap putAll() method to put few values in a Map. We've created a Map object of Integer,String pair. Then few entries are added using put() method and then map is printed. A new map is populated using putAll() method and then printed.

 package com.tutorialspoint; import java.util.HashMap; public class HashMapDemo { public static void main(String args[]) { // create hash map HashMap<Integer,String> newmap = new HashMap<>(); HashMap<Integer,String> newmap2 = new HashMap<>(); // populate hash map newmap.put(1, "tutorials"); newmap.put(2, "point"); newmap.put(3, "is best"); System.out.println("Map elements: " + newmap); newmap2.putAll(newmap); System.out.println("Map elements: " + newmap2); } } 

Output

Let us compile and run the above program, this will produce the following result.

 Map elements: {1=tutorials, 2=point, 3=is best} Map elements: {1=tutorials, 2=point, 3=is best} 

Adding multiple key,value pairs in a HashMap of Integer, Student Pair Example

The following example shows the usage of Java HashMap putAll() method to put few values in a Map. We've created a Map object of Integer,Student pair. Then few entries are added using put() method and then map is printed. A new map is populated using putAll() method and then printed.

 package com.tutorialspoint; import java.util.HashMap; public class HashMapDemo { public static void main(String args[]) { // create hash map HashMap<Integer,Student> newmap = new HashMap<>(); HashMap<Integer,Student> newmap2 = new HashMap<>(); // populate hash map newmap.put(1, new Student(1, "Julie")); newmap.put(2, new Student(2, "Robert")); newmap.put(3, new Student(3, "Adam")); System.out.println("Map elements: " + newmap); newmap2.putAll(newmap); System.out.println("Map elements: " + newmap2); } } class Student { int rollNo; String name; Student(int rollNo, String name){ this.rollNo = rollNo; this.name = name; } @Override public String toString() { return "[ " + this.rollNo + ", " + this.name + " ]"; } } 

Output

Let us compile and run the above program, this will produce the following result.

 Map elements: {1=[ 1, Julie ], 2=[ 2, Robert ], 3=[ 3, Adam ]} Map elements: {1=[ 1, Julie ], 2=[ 2, Robert ], 3=[ 3, Adam ]}