Interface

Question 1

What is Interface?

Answer 1

Interfaces group similar functionality and capabilities of different classes together. They model “act as” relationship

Question 2

Do all methods declared in Interface need to be defined?

Answer 2

Yes, Interfaces are contracts that classes agree to. If classes don’t implement all the methods then the compiler will give an error. Interfaces cannot be instantiated.

Question 3

Should signature in classes implementing interfaces be the same?

Answer 3

Signature(name and number/type of arguments) should be the same in class-defined methods.

Question 4

What is an override?

Answer 4

Override is an annotation and has no effect on how code behaves. It is just a signal to the compiler and to anyone who is reading the code.

Question 5

Why should we use @override?

Answer 5

1) If the programmer makes any mistake such as wrong method name, wrong parameter types while overriding, you would get a compile-time error. By using this annotation you instruct the compiler that you are overriding this method. If you don’t use the annotation then the sub-class method would behave as a new method (not the overriding method) in sub class.

Question 6

How many interfaces can a class implement?

Answer 6

A class can implement multiple interfaces. Implementing class must define every single method in each of its interfaces.

Question 7

What all you can have in the Interface body?

Answer 7

Abstract methods: Methods that are only declared do not need to explicitly mention as abstract
Default methods
Static methods
Constant declaration
By default every member of an interface is public.