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In this lesson we will learn about Abstract Classes and Abstract Methods in Java programming langauge.

Abstract Methods
An abstract method is a method that is declared in a (super)class, but not defined. In order to be instantiated, a subclass must provide the definition.

Abstract Classes
An abstract class is any class that includes an abstract method. It is similar to Pure virtual in C++. If a class includes an abstract method, the class must be declared abstract, too.

Code Example:

abstract class AbstractClass { 
   abstract public void Print(); 
   // no body, just the function header 
}
 
class MyConcreteClass extends AbstractClass { 
   public void Print() { 
   // actual code goes here 
   }
}

Important points to be remembered:

An abstract class cannot be instantiated.
A subclass of an abstract class that does not provide bodies for all abstract methods must also be declared abstract.
A subclass of a non-abstract class can override a (non-abstract) method of its superclass, and declare it abstract. In that case, the subclass must be declared abstract.

Next >>> Lesson No. 12: Java Interfaces