This question already has answers here:
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.
Related
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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
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.
This question already has answers here:
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This modifier is obsolete and should not be used in new programs.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'.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Java abstract interface
Why do Java developers use public abstract for interfaces? Interfaces are abstract by default.
For example:
public abstract interface test{
…
}
It's not necessary. According to JLS:
9.1.1.1. abstract Interfaces
Every interface is implicitly abstract.
This modifier is obsolete and should not be used in new programs.
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.