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

43560 square feet., calculate the size of the tract of land by the size of ...

calculate the size of the tract of land by the size of an acre to get the number of acres.

2D arrays, write an application that stores at least five different departm...

write an application that stores at least five different department and supervisor names in a two dimensional array

Performance of a java application, How can I improve the performance of a ...

How can I improve the performance of a java application , describe the java optimization techniques?

Write the java rmi interface definition, In the programming assignments, yo...

In the programming assignments, you are going to develop a simple distributed ticket reservation system (DTRS). This system is used by customers (with unique 6-digit customerID s)

Application for minesweeper, This program will help you start doing GUI pro...

This program will help you start doing GUI programming, and is a good example of 2D arrays. Mine Sweeper is a classic game that is played on a 2D grid of cells. At the beginning of

Applet, how to create a face with nose using applet

how to create a face with nose using applet

Why hub is used in networks, Why hub is used in networks? Hub is networ...

Why hub is used in networks? Hub is networking equipment and a device that connects various computers to form a network. In a network the NIC translates the message within elec

Cyclos ussd and mobile banking ivr module, Cyclos USSD and mobile banking I...

Cyclos USSD and mobile banking IVR module Project Description: We previously have a Cyclos mobile banking solution deployed on our server with SMS banking module. The solu

Padovan series, write a program in java using array and scanner class to ge...

write a program in java using array and scanner class to generate padovan series

Write down html or javascript code to declare array, Write down HTML or Jav...

Write down HTML or JavaScript code for the following requirements: Declare an Array along with the identifier SUBJECT having length 5. Assign subsequent values to the array par

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