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

How to evaluate two words similarity, I need to get how to start the java p...

I need to get how to start the java program to evaluate the simillarity.

What is jdbc exactly, What is JDBC exactly? Describe the steps required to ...

What is JDBC exactly? Describe the steps required to execute a SQL query using JDBC.

#title.swithcase, 2. Problem Description: A Java program needs to be writte...

2. Problem Description: A Java program needs to be written to display the result of following operations based input character. The table for input character with operations is : I

Write an application for a video store, Do you provides a Complete source C...

Do you provides a Complete source Codes for this application: " a. Write an application for a video store. Place the names of 10 of your favorite movies in a combo box. Let the use

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

Application for software tracking system, Talent agencies like ICM, CAA and...

Talent agencies like ICM, CAA and Paradigm represent writers, directors and actors (among other talent).  These agencies take in hundreds of millions of dollars a year collecting 1

Write a java windowed application, For this assignment, you will write a Ja...

For this assignment, you will write a Java windowed application to do online quiz on general knowledge and the application also displays the quiz result. Overview of the applic

Explain testing objects for equality in java, Explain Testing Objects for E...

Explain Testing Objects for Equality in java? , = can only be used with numbers and characters. They cannot be used with Strings, booleans, arrays or other compound types sin

Write a short Java application that stores words in an Array, Write a short...

Write a short Java application that stores words in an Array or ArrayList. You get to pick the number of words to store. Generate a random number between 0 (inclusive) and the leng

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