Abstract methods do not provide implementations.

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

Constructors and static methods can be declared as abstract.

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

An abstract class normally contains one or more abstract methods.

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

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