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

Build encyption decryption code, Hi, For my network and security class. I ...

Hi, For my network and security class. I have a project where I need to create a program that take an input and encrypts it and then you can also enter that value into another tex

What are the usages of package in java? , It helps to resolve naming confli...

It helps to resolve naming conflicts when different packages have classes with the same names. This also helps you prepare files within your project. As define : java.io package d

What is the comparable interface, What is the Comparable interface? Com...

What is the Comparable interface? Comparable interface is used to sort arrays and collections of objects using collections.sort() and java.utils. Objects of the class implement

Assignments, Define a function that will take a box type of object as argum...

Define a function that will take a box type of object as argument and return a box object whose dimension is 10 times more than the object

What are synchronized methods and synchronized statements, What are synchro...

What are synchronized methods and synchronized statements? Synchronized methods are methods that are used to control access to an object. A thread only implements a synchronize

Android apk for 3g dongles support, ANDROID APK for 3G dongles support P...

ANDROID APK for 3G dongles support Project Description: We want someone who will modify this Android app or code a similar one. The App function is to let Android tablet P

Beam, program for hinged beam

program for hinged beam

Define testing with respect to programming, Define testing with respect to ...

Define testing with respect to programming? Testing is the process through that we try to determine the presence defects in a program. Testing is an significant step in soft

Describe tostring() methods, Describe toString() Methods ? Print method...

Describe toString() Methods ? Print methods are general in some languages, but most Java programs operate differently. You can use System.out.println() to print any object. The

Using the Case Study supplied, The report: Your report must describe the re...

The report: Your report must describe the requirements of the application, outline the design of the solution, and provide a testing procedure to prove the application works. In yo

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