Explain the equals() method, JAVA Programming

Assignment Help:

Explain the equals() method

The equals() method of java.lang.Object acts the similar as the == operator; that is, it tests for object identity rather than object equality. The implicit contract of the equals() method, thus, is that it tests for equality rather than identity. Therefore most classes will override equals() along with a version that does field through field comparisons before deciding while to return true or false.

To elaborate, an object created through a clone() method (that is a copy of the object) should pass the equals() test if neither the original nor the clone has changed because the clone was created. Therefore the clone will fail to be == to the original object.

For instance, here is an equals() method you could use for the Car class. Two cars are equal if and only if their license plates are equal, and that's what this techniques tests for.
public boolean equals(Object o) {

if (o instanceof Car) {
Car c = (Car) o;
if (this.licensePlate.equals(c.licensePlate)) return true;
}
return false;
}
This example is particularly interesting since it demonstrates the impossibility of writing a useful generic equals() method in which tests equality for any object. It is not sufficient to easily test for equality of all the fields of two objects. It is whole possible that some of the fields might not be relevant to the test for equality as in this instance where changing the speed of a car does not change the in fact car that's referred to.

Be careful to prevent this common mistake when writing equals() methods:
public boolean equals(Car c) {

if (o instanceof Car) {
Car c = (Car) o;
if (this.licensePlate.equals(c.licensePlate)) return true;
}
return false;

}
The equals() method must permit tests against any object of any class, not simply against other objects of the similar class (Car in this example.)

You do not requires to test whether o is null. null is never an instance of any class. null instanceof Object returns false.


Related Discussions:- Explain the equals() method

Why do we call javascript an object-based language, Why do we call JavaScri...

Why do we call JavaScript an Object-based Language? In java language an JavaScript shares several similarities with object-oriented languages, and thus is known as an object-ba

Project on web service with complex data, This project is based on the team...

This project is based on the teams example of chapter 1. Instead of teams, you will consider employees working in a department in a company. (Departments and employees are analog

Define the type casting?, Type casting defines treating a variable of one t...

Type casting defines treating a variable of one type as though it is another type. When up casting primitives as given below from left to right, automatic conversion happens. Bu

What is jsp page, A JSP page is a text-based document that having two types...

A JSP page is a text-based document that having two types of text: static template data, which can be expressed in any text-based format like HTML, SVG, WML, and XML, and JSP eleme

Java rmi client implement and web service client-side steps, What is the na...

What is the name of the services you have chosen? What do they do? What is the name of the publisher? Provide details if you are developing your own service(s). There are variou

RatinalAssignment, 1. Make a class Rational to provide at least following m...

1. Make a class Rational to provide at least following methos and constructors: Rational r1= new Rational (3,5); Rational r2= new Rational (4,7); Rational r3=r1.add(r2);

Java identifiers, 1. Which of the following are not valid Java identifiers,...

1. Which of the following are not valid Java identifiers, and why? (a) wolVes (b) United(there is only one) (c) 87 (d) 5 3 (e) Real ale (f) isFound?by 2. A cla

Describe the if statement in java, Describe the if statement in Java ? ...

Describe the if statement in Java ? All but the most trivial computer programs required to form decisions. They test a condition and operate in a different way based on the out

What is the point-to-point model in jms, A point-to-point model is based on...

A point-to-point model is based on the concept of a message queue: Senders send messages into the queue, and the receiver reads messages from this queue. In the point-to-point mode

Design and implement online food delivery system, You are required to  desi...

You are required to  design & implement  online  food delivery  system  using Java RMI technology.  This involves writing both the server and the client program(s). Client programs

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd