Interface declaration in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an interface in Java?

An interface in Java is a blueprint that defines a set of abstract methods (methods without a body) that a class can implement. It specifies what a class must do, but not how.

beginner

How do you declare an interface in Java?

You declare an interface using the keyword interface followed by the interface name and a block containing method signatures. Example:<br>

public interface MyInterface {
  void myMethod();
}

intermediate

Can interfaces have method bodies in Java?

Since Java 8, interfaces can have default methods with bodies using the default keyword, and static methods with bodies. But regular abstract methods do not have bodies.

beginner

What keyword does a class use to implement an interface?

A class uses the <code>implements</code> keyword to promise it will provide code for all the methods declared in the interface.

intermediate

Can an interface extend another interface?

Yes, an interface can extend one or more other interfaces using the extends keyword. This allows combining multiple interfaces into one.

Which keyword is used to declare an interface in Java?

A interface

B class

C implements

D extends

The keyword interface is used to declare an interface.

How does a class promise to follow an interface's rules?

A overrides

B extends

C inherits

D implements

A class uses implements to promise it will provide all methods from the interface.

Can interfaces have method bodies in Java 8 and later?

A Only for abstract methods

B No, never

C Yes, for default and static methods

D Only for private methods

Since Java 8, interfaces can have default and static methods with bodies.

Which of these is true about interfaces?

A Interfaces define method signatures without bodies by default

B Interfaces can contain constructors

C Interfaces cannot extend other interfaces

D Interfaces can be instantiated directly

Interfaces define method signatures without bodies by default.

What keyword allows an interface to inherit from another interface?

A implements

B extends

C inherits

D uses

Interfaces use extends to inherit from other interfaces.

Explain how to declare an interface and how a class uses it.

Think about the keywords and what each part means.

Describe the difference between abstract methods and default methods in interfaces.

Consider what changed in Java 8.