Java IdentityHashMap put() method

The put(K key, V value) method of the Java IdentityHashMap class is used to link the specified key with a specified value in the calling IdentityHashMap.

Syntax

Parameters

Key - The key with which the specified value is to be linked.

Value - The value which is to be linked with the specified key.

Return

The previous value associated with the key or null if there was no linkage for the specified key.

Example 1

import java.util.IdentityHashMap;

public class IdentityHashMapPutExample1 {
    public static void main(String[] args) {
   //Creating an object of IdentityHashMap class
   IdentityHashMap<String,Integer> map = new IdentityHashMap<String,Integer>(6);
   
   //Putting key-value pairs inside map
   System.out.println(map.put("Java", 1));
   System.out.println(map.put("is", 12));
   System.out.println(map.put("is", 2));
   System.out.println(map.put("the", 3));
   System.out.println(map.put("best", 4));
   System.out.println(map.put("best", 4));
   System.out.println(map.put("programming", 5));
   System.out.println(map.put("language", 6));
   
   //All the Linkages in the IdentityHashMap
   System.out.println(map);
}
}

Output:

null
null
12
null
null
4
null
null
{Java=1, the=3, language=6, programming=5, best=4, is=2}

Example 2

import java.util.IdentityHashMap;

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 IdentityHashMapPutExample2 {
    public static void main(String[] args) {
        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);
        
         //Creating an instance of IdentityHashMap
        IdentityHashMap<Integer,Student> map = new IdentityHashMap<Integer,Student>(5);

        //Inserting values in IdentityHashMap
        System.out.println(map.put(1,stud1));
        System.out.println(map.put(2,stud2));
        System.out.println(map.put(3,stud3));
        System.out.println(map.put(4,stud4));
        
        System.out.println(map.keySet());
}
}

Output: