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Interface vs 100% abstract class [duplicate]

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Interface vs Abstract Class (general OO)
(36 answers)
Closed 5 years ago.
If we can have 100% abstract class with all abstract methods that will work equivalent to Interface.Why we have interface and how it is better than 100% abstract class???

A class can only inherit from one abstract class, but it can implement as many interfaces as its developer wants to. That's why you should prefer interfaces over abstract classes, unless you have to provide an implementation of a method.

Why only public methods are allowed in an interface? [duplicate]

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Protected in Interfaces
(15 answers)
Closed 6 years ago.
Why does java force interface methods to be public and how does abstract class differs from an interface?

A quick response is:
All the interface methods must be overriden, for that they must be public.
Abstract classes can be extended by other classes, the interfaces only can be implemented by classes and inherited by other interfaces.
You can get a lot more information here: http://www.javaworld.com/article/2077421/learn-java/abstract-classes-vs-interfaces.html

Why define a abstract interface in Java [duplicate]

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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This modifier is obsolete and should not be used in new programs.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'.

Java - Is every interface an abstract class? [duplicate]

This question already has answers here:
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.

Abstract and Interface in java [duplicate]

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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.