This question already has answers here:
When do you use Java's #Override annotation and why?
(27 answers)
Should we #Override an interface's method implementation?
(15 answers)
Closed 4 years ago.
When extending an abstract class I understand why you would have to over ride some methods. But when it comes to interfaces I do not understand why it must be done. If all methods of an interface must be implemented, what is the use of overriding them?.
Im talking about the #Override annotation.
Using #Override is purely optional. You don't have to use it. If you do, using #Override when implementing an interface has more or less the same reasoning as using it when extending an abstract class. In a nutshell, it prevents stupid mistakes - if an interface is changed, it forces you to change your class accordingly, instead of just tacking on the "new" methods you suddenly need to implement.
Related
This question already has answers here:
What is the point of using abstract methods?
(7 answers)
What is the purpose of an abstract method?
(5 answers)
Abstract class and methods, Why?
(4 answers)
Closed 5 years ago.
I'm Currently reading Head First Java, I'm learning about abstract classes and methods, it's all making wonderful sense at the moment but one thing is puzzling me.
The book states that if declaring an abstract method in an abstract class then this method must be overridden by any of the sub-classes, which initially made sense when i learned that abstract methods have no body, my question then is this:
If an abstract method has no body and must also be overridden by any sub-classes, what is the point in declaring an abstract method in the first place, the programmer still has to create the overridden method in each and every sub-class, so why not just forget about the abstract method which has no body anyway, thus alleviating the need to override, it just seems like less code to type or if looking at it the other way more code to type??
Thanks.
D.
This question already has answers here:
Do/can abstract classes replace interfaces? [duplicate]
(11 answers)
what is the actual use of interface in java? [duplicate]
(6 answers)
Closed 7 years ago.
In java there is interface which having only abstract method means method declration only and those methods are implement in class that implement interface so why to use interface which has only declaration .This question is asked in interview.
Interfaces are used for only declaration of methods because it can achieve multiple behavior. It is the class's responsibility to implement the interfaces and define their methods as they desire.
Interfaces allow same methods to be implemented in different manner by implementing classes, which allows you to achieve behavioral facility.
For understanding sake, you can consider interfaces exist so you can achieve behavioral approach for your application, and class exist to achieve characteristic approach.
This question already has answers here:
Implementing Incompatible Interfaces [duplicate]
(2 answers)
Implementing two interfaces in a class with same method. Which interface method is overridden?
(8 answers)
Closed 7 years ago.
Below code,
interface I3{
boolean abc();
};
interface I2{
void abc();
};
public class Example1 implements I3, I2{
#Override
public void abc() {
//Eclipse IDE picked this unimplemented method with the compiler error
}
}
Is it the responsibility of a programmer to not get into this situation?
Why Java has allowed an interface extending multiple interfaces? when java has already avoided similar problem of a class inheriting multiple super classes?
In case of similar constants inherited from multiple interfaces, interfacename.constantname in a subclass avoids ambiguity.
Yes it is definely the responsability of the programmer to not get into this situation.
Interface is a way to have multiple inheitence, we must not confuse the JVM with these kind of conflicts.
because both abc()method have the same signature (return type is not a part of method signature) and java can't make difference between theme and this situation cause a conflict
This question already has answers here:
What is an abstract class? [duplicate]
(13 answers)
Closed 8 years ago.
Why one sometimes writes
abstract void etwas();
codcodecode
void etwas()
{
return;
}
Instead of skipping the single declaration? In which cases is it necessary?
In the same class, this almost never happens.
It happens when you have an abstract class, which defines an abstract method. You do so when you want to make sure that anyone who extends this abstract class, will be forced to provide his own implementation for this abstract method. Otherwise a compile error occurs.
This question already has answers here:
Defining an abstract class without any abstract methods
(12 answers)
Use of an abstract class without any abstract methods
(7 answers)
Closed 9 years ago.
can any one please explain the scenario when A class may be declared abstract even if it has no abstract methods. i have tried in many websites but i did not found it.Thanks a lot.
Broadly, this would be because the class provides concrete implementations of functionality but should not itself be instantiated. For example, an AbstractWidget in a price calculator may not be suitable to directly instantiate, but it has concrete implementations of certain widget functionality like being rearranged. The expectation is that the subclass adds new methods altogether, or overrides the ones already declared.