What is the use of equals method in Java?

Posted On: 2023-06-02 01:16:11 Core Java

Equals method is used when we compare two objects. Default implementation of equals method is defined in Object class. The implementation is similar to == operator. Two object references are equal only if they are pointing to the same object.

== comparison operator checks if the object references are pointing to the same object. It does NOT look at the content of the object.

class Client {
private int id;
public Client(int id) {
this.id = id;
}
}

== comparison operator checks if the object references are pointing to the same object. It does NOT look at the content of the object.

Client client1 = new Client(25);
Client client2 = new Client(25);
Client client3 = client1;
//client1 and client2 are pointing to different client objects.
System.out.println(client1 == client2);//false
//client3 and client1 refer to the same client objects.
System.out.println(client1 == client3);//true

//similar output to ==
System.out.println(client1.equals(client2));//false
System.out.println(client1.equals(client3));//true

We need to override equals method, if we would want to compare the contents of an object

class Client {
private int id;
public Client(int id) {
this.id = id;
}
@Override
public boolean equals(Object obj) {
Client other = (Client) obj;
if (id != other.id)
return false;
return true;
}
}

Consider running the code below:
Client client1 = new Client(25);
Client client2 = new Client(25);
Client client3 = client1;
//both id's are 25
System.out.println(client1.equals(client2));//true
//both id's are 25 System.out.println(client1.equals(client3));//true