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Can an interface have concrete methods?
Interfaces cannot have any concrete methods. If you need the ability to have abstract method definitions and concrete methods then you should use an abstract class.
Is it is necessary to implement all methods of interface in concrete class?
Yes, it is mandatory to implement all the methods in a class that implements an interface until and unless that class is declared as an abstract class. Declare the class as an abstract class, as a result, forces you to subclass the class (and implement the missing methods) before you can create any objects.
CAN interface have normal methods?
Like a class, an interface can have methods and variables, but the methods declared in an interface are by default abstract (only method signature, no body). If a class implements an interface and does not provide method bodies for all functions specified in the interface, then the class must be declared abstract.
Why is it not allowed to declare a public interface in Java?
Even you do not state a method as a public in interface it is public. But in your class, you have declared this method as package private. It is not allowed, because it reduces the visibility of the implemented method.
Why do all interface methods have to be public?
All interface methods are public by default (even if you don’t specify it explicitly in the interface definition), so all implementing methods must be public too, since you can’t reduce the visibility of the interface method. In the interface you have method getGait() declared as public.
What is the point of having every service class have an interface?
An interface exposes a public contract for your service, without implementation details such as private methods or attributes. Note that “public” when using internal services (as in your case) refers to the actual users of said services, including — but not limited to — other programmers and internal services!
What’s the point of an interface in Java?
Java interfaces aren’t just about mockability (though of course, that is a factor). An interface exposes a public contract for your service, without implementation details such as private methods or attributes.