An abstract class normally contains one or more abstract methods.

Abstract methods do not provide implementations.

Constructors and static methods can be declared as abstract.

A class can be made abstract by declaring it with the keyword abstract.

The declaration of an abstract method in Java can be like this Java statement, public abstract void goulin();

A class that contains abstract methods must be an abstract class even if that class contains some non-abstract (i.e. concrete) methods.

Each concrete subclass of an abstract superclass must also provide concrete implementations of each of the superclass's abstract methods.