Why an interface can not implement another interface

Question

What I mean is   interface B        interface A extends B          allowed    interface A implements B          not allowed   I googled it and I found this      implements denotes defining an implementation for the methods of an interface  However interfaces have no implementation so that s not possible    However  interface is an 100  abstract class  and an abstract class can implement interfaces  100  abstract class  without implement its methods  What is the problem when it is defining as  interface     In details   interface A       void methodA       abstract class B implements A       we may not implement methodA   but allowed  class C extends B      void methodA         interface B implements A       not allowed     however  interface B    100 abstract class B

User · Answer

Conceptually there are the two  domains  classes and interfaces  Inside these domains you are always extending  only a class implements an interface  which is kind of  crossing the border   So basically  extends  for interfaces mirrors the behavior for classes  At least I think this is the logic behind  It seems than not everybody agrees with this kind of logic  I find it a little bit contrived myself   and in fact there is no technical reason to have two different keywords at all

User · Answer

implements means a behaviour will be defined for abstract methods  except for abstract classes obviously   you define the implementation   extends means that a behaviour is inherited   With interfaces it is possible to say that one interface should have that the same behaviour as another  there is not even an actual implementation  That s why it makes more sense for an interface to extends another interface instead of implementing it     On a side note  remember that even if an abstract class can define abstract methods  the sane way an interface does   it is still a class and still has to be inherited  extended  and not implemented

User · Answer

Hope this will help you a little what I have learned in oops  core java  during my college   Implements denotes defining an implementation for the methods of an interface  However interfaces have no implementation so that s not possible  An interface can however extend another interface  which means it can add more methods and inherit its type   Here is an example below  this is my understanding and what I have learnt in oops   interface ParentInterface            void myMethod           interface SubInterface extends ParentInterface            void anotherMethod            and keep one thing in a mind one interface can only extend another interface and if you want to define it s function on some class then only a interface in implemented eg below  public interface Dog       public boolean Barks         public boolean isGoldenRetriever        Now  if a class were to implement this interface  this is what it would look like   public class SomeClass implements Dog       public boolean Barks         method definition here             public boolean isGoldenRetriever         method definition here           and if a abstract class has some abstract function define and declare and you want to define those function or you can say implement those function then you suppose to extends that class because abstract class can only be extended  here is example below   public abstract class MyAbstractClass        public abstract void abstractMethod        Here is an example subclass of MyAbstractClass   public class MySubClass extends MyAbstractClass        public void abstractMethod             System out println  My method implementation

User · Answer

implements means implementation  when interface is meant to declare just to provide interface not for implementation   A 100  abstract class is functionally equivalent to an interface but it can also have implementation if you wish  in this case it won t remain 100  abstract   so from the JVM s perspective they are different things   Also the member variable in a 100  abstract class can have any access qualifier  where in an interface they are implicitly public static final

User · Answer

Interface is the class that contains an abstract method that cannot create any object Since Interface cannot create the object and its not a pure class  Its no worth implementing it

User · Answer

However  interface is 100  abstract class and abstract class can   implements interface 100  abstract class  without implement its   methods  What is the problem when it is defining as  interface      This is simply a matter of convention   The writers of the java language decided that  extends  is the best way to describe this relationship  so that s what we all use   In general  even though an interface is  a 100  abstract class   we don t think about them that way   We usually think about interfaces as a promise to implement certain key methods rather than a class to derive from   And so we tend to use different language for interfaces than for classes   As others state  there are good reasons for choosing  extends  over  implements

User · Answer

Interface is like an abstraction that is not providing any functionality  Hence It does not  implement  but extend the other abstractions or interfaces

[java] Why an interface can not implement another interface?

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