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

About state and behavier of two different object, two different object may...

two different object may have chance to have same behavier but property must be different why?

Java program to scrape, Java Program to Scrape, Data Mine Project Descri...

Java Program to Scrape, Data Mine Project Description: I need to data scrape/ mine data from a website and do some data processing. Skills required: Java, Data Mining,

OOP, differentiate between states and behaviors of n object

differentiate between states and behaviors of n object

Want to run program on netbeans, Want to run program on netbeans I tried my...

Want to run program on netbeans I tried my best still wont be able to do it

Constructors, how do I use constructors in java and how do I apply them

how do I use constructors in java and how do I apply them

Write the hashcode() method of java.lang.object, Write the hashCode() metho...

Write the hashCode() method of java.lang.Object Anytime you override equals() you should also override hashCode(). The hashCode() method should ideally return the similar int f

JAVA Programming, Im not in the line of computer science.But i would like t...

Im not in the line of computer science.But i would like to have some knowledge about the computer language "JAVA".I aldredy learns the computer languages "C,C++".So kindly help me

Explain the phase compile- java program development, Explain the phase Comp...

Explain the phase Compile- Java Program Development In Phase 2, programmer gives the command javac to compile the program. Java compiler translates the java program into byte

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