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Java abstract interface
(9 answers)
Closed 9 years ago.
As we know, interface is to define some method, but some interface defined as a abstract interface, but why ?
for example:
public abstract interface Test{
}
what is the advantage for using abstract to define a interface?
There is no need to add that abstract key word. It's redundant there.
Interfaces are implicitly abstract.
Language Spec JLS# 9.1.1.1 abstract Interfaces
Every interface is implicitly abstract.
This modifier is obsolete and should not be used in new programs.
refer to http://docs.oracle.com/javase/tutorial/java/IandI/createinterface.html for the same.
Also see https://stackoverflow.com/a/18778307/805378 to get the difference between abstract and interface.
to make a class 100% abstract without using 'abstract'.
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Interface vs Abstract Class (general OO)
(36 answers)
Closed 9 years ago.
In Java every method in an interface is implicitly abstract. But when at least one method in a class is abstract, that means that this class is abstract. Does that mean, that every interface is an abstract class?
I guess in some sort of way, yes. An abstract class can be used as an interface.
The issue is that a class can only extends on other class. A class can implements any number of interfaces.
So while abstract classes are similar to interfaces they are very different in reality.
Does that mean, that every interface is an abstract class?
No. An interface (in Java 7 and earlier) can have no method implementations and can define no instance fields. An abstract class can do both. These are just some of the substantive differences.
But when at least one method in a class is abstract.
But its not a class,Its interface.
Instead you can say it's an abstract interface.
And finally :An interface is abstract by definition.
Yes when i decompiled a interface it had the modifier public abstract interface, and by definition they must be abstract to contain abstract methods.
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Closed 10 years ago.
Possible Duplicate:
When shall we go for interface or abstract class in Java?
I have a doubt in java.I know about the interfaces and abstract classes.But I want to know specifically when to use interface and when to use abstract classes in java and android.I want a practical explanation with real world example not a theoretical or documented one.
Thanks.
The key difference is that you can implement multiple interfaces in a
class, but only extend a single abstract class.
Interface is used when you only want to declare which methods and members a class MUST have. Anyone implementing the interface will have to declare and implement the methods listed by the interface.
If you also want to have a default implementation, use abstract class. Any class extending the abstract class will have to implement only its abstract methods and members, and will have some default implementation of the other methods of the abstract class, which you may override or not.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Interface or abstract class?
Abstract and Interface in java
I am still a student in Java and i came across abstract class and interface.
now when you create an abstract class you write methods like this:
public abstract void something();
but when you create a method in your interface it looks like this:
public void something();
Now im not blind i can see that there is some difference also i do know that you extend an abstract class and you implement an interface.
But can someone tell me what the difference is maybe an example of where you would use one over the other?
There's no difference between those two routines. The difference lies in that abstract classes can contain common logic used for all implementations while interfaces cannot.
"Abstract" basically means that the method has no implementation. The implementation has to be provided by subclasses. As a consequence, one cannot create instances of classes having abstract methods.
Now interfaces in Java are just a collection of method signatures. They cannot contain implementations by design. Thus, the abstract keyword would be redundant. One cannot create instances of interfaces, only of concrete classes that implement the interface.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Interface vs Abstract Class (general OO)
When to use abstract class or interface?
Can you provided implementations on a abstract class?
what's the difference between these two?
and when will I know when will I know to use them?
This pages gives a good comparison: http://download.oracle.com/javase/tutorial/java/IandI/abstract.html . You could have found it with a very quick google search.
Interface is used for defining a contract. Abstract classes are used for defining some methods which are common to all descendants and possibly some methods which will differ(they will be abstract). With interfaces or abstract classes polymorphism is reached.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Interface vs Abstract Class (general OO)
I am little bit familiar with the terms Abstract class and the interface.
But i want to know in which situation i have to use the interface and in which condition the abstract class.
Thanks
Interface vs Abstract Class should be a useful read.
In short, Abstract Classes are meant to be extended, as in you're giving someone a base to work off of. Interfaces ensure that things have a common way of interacting with one another without having to worry about the inside details.
Simple answer: you can implements many interfaces, but can only inherit from one class, so if you want to inherit some logic, you should use Abstract Class, otherwise Interface is more extensible.