This question already has answers here:
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
Related
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.
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:
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:
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.