The HashMap class is similar to the IdentityHashMap class. The IdentityHashMap implements the Map interface using Hashtable, and when comparing keys, it uses reference-equality rather than object-equality (and values). This class is not intended to be a general-purpose Map implementation. This class is used when the user wants to compare objects by reference. It is part of java.util package.

Constructors of the IdentityHashMap class:

Methods of AbstractList Class:

Example:

// Java code to illustrate
// adding elements to IdentityHashMap
import java.util.*;

public class Coderz{

	public static void main(String[] args)
	{
		// Creating an empty IdentityHashMap
		Map<Integer, String> id
			= new IdentityHashMap<Integer, String>();

		// Mapping string values to int keys
		// using put() method
		id.put(10, "A");
		id.put(15, "4");
		id.put(20, "Java");
		id.put(25, "Month");
		id.put(30, "cake");

		// Displaying the IdentityHashMap
		System.out.println("Initial Mappings are: "
						+ id);

		// Inserting existing key along with new value
		// previous value gets returned and stored in
		// returned_value
		String returned_value
			= (String)id.put(20, "All");

		// Verifying the returned value
		System.out.println("Returned value is: "
						+ returned_value);

		// Displaying the new map
		System.out.println("New map is: " + id);

		// Creating a new Identityhash map and copying
		Map<Integer, String> new_Id
			= new IdentityHashMap<Integer, String>();
		new_Id.putAll(id);

		// Displaying the final IdentityHashMap
		System.out.println("The new map: "
						+ new_Id);
		 returned_value =(String)id.remove(10);
 
        // Verifying the returned value
        System.out.println("Returned value is: " +
                                    returned_value);
                                     Iterator<IdentityHashMap.Entry<Integer, String> >
            itr = id.entrySet().iterator();
 
        // The hasNext() method is used to check if there is
        // a next element The next() method is used to
        // retrieve the next element
        while (itr.hasNext()) {
            IdentityHashMap.Entry<Integer, String> entry
                = itr.next();
            System.out.println("Key = " + entry.getKey()
                               + ", Value = "
                               + entry.getValue());
        }
	}
}

Output:

Initial Mappings are: {30=cake, 10=A, 15=4, 25=Month, 20=Java}
Returned value is: Java
New map is: {30=cake, 10=A, 15=4, 25=Month, 20=All}
The new map: {30=cake, 10=A, 15=4, 25=Month, 20=All}
Returned value is: A
Key = 30, Value = cake
Key = 15, Value = 4
Key = 25, Value = Month
Key = 20, Value = All

Note: also read about the EnumSet in Java

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Rabecca Fatima

Staying up to the mark is what defines me. Hi all! I’m Rabecca Fatima a keen learner, great enthusiast, ready to take new challenges as stepping stones towards flying colors.