Define an abstract class with reference to Java.

An abstract class is a class in java which contains the abstract keyword in its declaration. It can have both abstract and non-abstract methods. The abstract class can have the public, private, protected, constant and default variables. This class needs to be extended and we need to implement the methods. This class can’t be instantiated. A class can be declared as an abstract class if it has at least one abstract method. An abstract class has at least one virtual function. Keyword “abstract” is used to make a class abstract.