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

What is lookupdispatchaction, The LookupDispatchAction is a subclass of Dis...

The LookupDispatchAction is a subclass of DispatchAction. It does a reverse lookup on the resource package to get the key and then gets the method whose name is associated with the

State about the jvm, State about the JVM? JVM is the acronym which ...

State about the JVM? JVM is the acronym which stands for 'Java virtual machine'. JVM provides execution environment. JVM isn't platform independent. JVM is Java

Project on image processing, Project Description: Computer vision and Im...

Project Description: Computer vision and Image processing project to extract book title Skills required: Java, C Programming

What is static in java, What is static in java? Static means one per cl...

What is static in java? Static means one per class, not one for each object no matter how many example of a class might exist. This means that you can use them without making a

Program that compute prime numbers, The purpose of this assignment is to gi...

The purpose of this assignment is to give you practice working with one dimensional arrays. It will also introduce you to one of the oldest mathematical algorithms in the world. No

How can we define a computer screen, How can we define a computer screen? ...

How can we define a computer screen? A computer screen is define as use to display output of computer to the user. Computer screen is consists of pixels.

We want the best java programmer, We want the best java programmer availabl...

We want the best java programmer available. Project Description: Java | Portlets| JSF Liferay (not essential but is preferable) Big Data and User online tools. Multilin

Describe the edit phase- java program development, Describe the Edit phase-...

Describe the Edit phase- Java Program Development Phase comprises editing a file. This is done with an editor program. Programmer types a java program using editor such as no

Write a program to add integer value, Write a program to add integer value?...

Write a program to add integer value? class AddInts { public static void main (String args[]) { int i = 1; int j = 2; System.out.println("i is " + i); System.out.println("

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