Java IdentityHashMap putAll() method

The putAll(Map<? extends K, ? extends V> m) method of the Java IdentityHashMap class is used to copy all the key-value pairs from the specified Map to the calling IdentityHashMap.

Syntax

Return

m - Map from which key-value pairs are to be copied

Example 1

import java.util.IdentityHashMap;
import java.util.Set;

public class IdentityHashMapPutAllExample1 {
    public static void main(String[] args) {
   //Creating an object of IdentityHashMap class
   IdentityHashMap<String,Integer> map1 = new IdentityHashMap<String,Integer>(6);
   IdentityHashMap<String,Integer> map2 = new IdentityHashMap<String,Integer>(6);
   
   //Putting key-value pairs inside map1
   map1.put("Java", 1);
   map1.put("is", 2);
   map1.put("the", 3);
   map1.put("best", 4);
   map1.put("programming", 5);
   map1.put("language", 6);
   
   //Displaying elements of map1
   System.out.println(map1);   
   
   //Checking if map2 is empty or not
   System.out.println(map2);
   
   //Copying all elements from map1 into map2
   map2.putAll(map1);
   
   //Displaying elements of map2
   System.out.println(map2);
}
}

Test it Now

Output:

{Java=1, the=3, language=6, programming=5, best=4, is=2}
{}
{Java=1, the=3, language=6, programming=5, best=4, is=2}

Example 2

import java.util.IdentityHashMap;
import java.util.Set;

class Student{
    private int roll;
    private String name;
    private int standard;
    
    public Student(int roll,String name,int standard){
        this.roll = roll;
        this.name = name;
        this.standard = standard;
    }
    
    public String disp(){
        return roll+" "+name+" "+standard;
    }
}

public class IdentityHashMapPutAllExample2 {
    public static void main(String[] args) {
        
        //Creating Objects of Student class
        Student stud1 = new Student(1 ,"Ram ",10);
        Student stud2 = new Student(2 ,"Shyam ",10);
        Student stud3 = new Student(3 ,"Aman ",12);
        Student stud4 = new Student(4 ,"Harsh ",12);
        Student stud5 = new Student(5 ,"Shivam",11);
        
        //Creating an instance of IdentityHashMap
        IdentityHashMap<Integer,Student> map1 = new IdentityHashMap<Integer,Student>(5);
        IdentityHashMap<Integer,Student> map2 = new IdentityHashMap<Integer,Student>(5);
        
        //Inserting the Student class objects into IdentityHashMap
        map1.put(1,stud1);
        map1.put(2,stud2);
        map1.put(3,stud3);
        map1.put(4,stud4);
        
        //Displaying elements of map1
        System.out.println(map1);
        
        //Checking if map2 is empty or not
        System.out.println(map2);
   
        //Copying all elements from map1 into map2
        map2.putAll(map1);
   
        //Displaying elements of map2
        System.out.println(map2);
}
}

Test it Now

Output:

{1=Student@70dea4e, 3=Student@5c647e05, 2=Student@33909752, 4=Student@55f96302}
{}
{1=Student@70dea4e, 3=Student@5c647e05, 2=Student@33909752, 4=Student@55f96302}

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