Abstract methods in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an abstract method in Java?

An abstract method is a method declared without a body (no implementation) using the abstract keyword. It must be implemented by subclasses.

beginner

Can you create an object of a class that contains an abstract method?

No, you cannot create an object of a class that has abstract methods because such a class is abstract and incomplete.

beginner

How do you declare an abstract method in Java?

Use the abstract keyword before the method signature and do not provide a method body. For example: abstract void myMethod();

intermediate

What must a subclass do if its superclass has abstract methods?

The subclass must provide concrete implementations (bodies) for all inherited abstract methods, or it must also be declared abstract.

intermediate

Why use abstract methods in Java?

Abstract methods define a contract for subclasses, ensuring they implement specific behaviors while allowing different implementations.

Which keyword is used to declare an abstract method in Java?

A private

B abstract

C static

D final

The abstract keyword declares a method without a body, requiring subclasses to implement it.

Can an abstract method have a method body in Java?

A Only if the class is abstract

B Yes, always

C No, never

D Only if the method is static

Abstract methods cannot have a body; they only declare the method signature.

What happens if a subclass does not implement all abstract methods from its abstract superclass?

A The subclass must be declared abstract

B The program runs but throws an error at runtime

C It compiles without errors

D The abstract methods are ignored

If a subclass does not implement all abstract methods, it must also be declared abstract.

Can you instantiate an abstract class directly?

A No, abstract classes cannot be instantiated

B Yes, if it has no abstract methods

C Yes, but only inside the same package

D Only if the constructor is public

Abstract classes cannot be instantiated directly because they may have incomplete methods.

Which of the following is true about abstract methods?

A They are always static

B They can be private

C They can have multiple implementations in the same class

D They must be implemented by subclasses

Abstract methods must be implemented by subclasses to provide specific behavior.

Explain what an abstract method is and why it is useful in Java.

Think about how abstract methods help define rules for subclasses.

Describe the rules a subclass must follow when inheriting abstract methods.

Focus on subclass responsibilities with abstract methods.