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

Explain pop, SMTP (Simple Mail Transfer Protocol) permits two mail servers ...

SMTP (Simple Mail Transfer Protocol) permits two mail servers to communicate using a easy language, and gives a step-by-step protocol for exchanging information. SMTP delivers m

What are the basic advantages of jms, JMS is asynchronous in nature. Theref...

JMS is asynchronous in nature. Therefore not all the pieces need to be up all the time for the application to function as a whole. Even if the receiver is down the MOM will kept th

Conversation to html, Conversation to HTML Project Description: We ha...

Conversation to HTML Project Description: We have inner pages to be transformed into html for travel domain. 1. Flight search page for one way and round trip 2. Bus res

Give a example of using tostring() methods, Give a example of Using toStrin...

Give a example of Using toString() Methods ? Below is a version of CarTest in which uses toString() and System.out.println() instead of printing the fields in a straight line

Pseudocodes, Draw a 5 inch square on the screen using pseudocode

Draw a 5 inch square on the screen using pseudocode

Create a general design for a class-implement and test, Objectives 1.  ...

Objectives 1.      To design and implement a simple class. 2.      To write a test program to create instances of your class and demonstrate its behaviour. 3.      To col

What is constructors and explain with an example, What is Constructors? Exp...

What is Constructors? Explain with an example? A constructor forms a new instance of the class. It initializes all the variables and does any work essential to prepare the clas

Why there is a need to use primary key in database, Why there is a need to ...

Why there is a need to use primary key in database ? Primary key is a constraint basically used in datdabase to uniquely identify the records in the database.

The fancy new French restaurant La Food is very popu, The fancy new French ...

The fancy new French restaurant La Food is very popular for its authentic cuisine and high prices. This restaurant does not take reservations. To help improve the efficiency of the

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