Interfaces and Abstract Classes Flashcards

Which keyword is used to declare an interface in Java?

Answer: interface

The `interface` keyword declares an interface in Java, defining a contract of method signatures without implementations.

Which keyword does a class use to adopt an interface?

Answer: implements

A class uses the `implements` keyword to adopt one or more interfaces and provide concrete implementations for their methods.

By default, all methods declared inside an interface are:

Answer: public and abstract

Interface methods are implicitly public and abstract, meaning any implementing class must provide a concrete implementation.

What happens if a class implements an interface but does not override all of its abstract methods?

Answer: The class must be declared abstract

If a class does not implement all abstract methods of an interface, it must itself be declared abstract; otherwise, the code will not compile.

Can a single class in Java implement more than one interface?

Answer: Yes, by listing them separated by commas after implements

Java allows a class to implement multiple interfaces by listing them after the `implements` keyword, separated by commas.

Which of the following is TRUE about variables declared inside an interface?

Answer: They are public, static, and final by default

Variables declared in an interface are implicitly public, static, and final — they are constants that cannot be changed.

Which of the following best describes the purpose of an interface in Java?

Answer: To define a contract specifying what methods a class must implement

An interface defines a contract — a set of method signatures — that any implementing class must fulfill, promoting abstraction and polymorphism.