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

Create an android application., We need to create an Android application. T...

We need to create an Android application. The application is about registering courses in a university, viewing grades, available courses and evaluating faculty members. Advisor

How to catch multiple exceptions explain with example, How to catch multipl...

How to catch multiple exceptions explain with example? If multiple blocks match the exception type, the first block in which matches the kinds of the exception catches it. pub

I need gpa calculating application, I need GPA calculating application P...

I need GPA calculating application Project Description: My project is one of the GPA calculating application, Colleges have 37 courses or departments, engineering results alw

How virtual communities are formed, How virtual communities are formed? How...

How virtual communities are formed? How these are different from other Communities? Give examples. Virtual Communities are interest-based communities. Members along with genera

How many bits are used to show unicode and ascii, How many bits are used to...

How many bits are used to show Unicode, ASCII, UTF-16, and UTF-8 characters? Unicode requires 16 bits and ASCII require 7 bits although the ASCII character set uses only 7 bits

Functions in javascript, These are the central working units of JavaScript....

These are the central working units of JavaScript. Almost all the scripting code employs one or more functions to obtain the desired result. If you desire your page to provide cert

Calculates number of negative and positive numbers in array, Question 3 ...

Question 3 Using this line: var posneg : array [1..15] of integer; Write a program that calculates the number of negative and positive numbers in the array. Users will

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

Differentiate between onload and onunload, Differentiate between onLoad and...

Differentiate between onLoad and onUnload? Onload executes the particular javascript code when a latest document is loaded into a windows. ONUnload executes he particular javas

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