What are the differences between class and abstract class?

Answer 1

Below is the main difference between the 3 components:

• Concrete class - Provides implementation for all its methods & also for methods from extended abstract classes or implemented interfaces
• Abstract class - Does not provide implementation for one or more of its methods
• Interface - Does not provide implementation for any of its methods

Answer 2

You cannot instantiate an object of an abstract class.

Example:

You might have two objects 'man' and 'woman' which inherit common characteristics (two eyes, a nose etc) from 'human'. You wouldn't want humans that are neither walking around so you make human an abstract class as you'll never need a human object.

Answer 3

Assume a "simple" class be a class without the keyword "abstract".

You cannot create an instance of an abstract class. An abstract class is intended to be inherited from (to be extended or derived from).

A "simple" class is a class that an instance can be created from (via new operator)

Answer 4

Normal variables or static variables are declared and use in class but abstract class had only static variables. You have declare and define the methods in class. But abstract class only allow for method declaration only. The abstract class like interface.

Answer 5

An Abstract class is a special kind of class that cannot be instantiated. It has one or more methods which are not implemented in the class. These methods are declared abstract and they do not contain any code inside them.

Ex:

abstract class Parent {

public abstract String getSon();

public abstract String getDaughter();

....

....

//More methods that contain specific behaviour/code in them

}

The above is an abstract class "Parent" that has a lot of functionality but it has declared two abstract methods which have no code inside them. Any class that has one or more abstract methods has to be abstract. This abstract class cannot be instantiated.

i.e., the below piece of code will not work. The code will not even compile.

Parent object = new Parent();

Purpose of Abstract Classes:

Abstract classes are generally used where you want an amount of behaviour to be used by the class that extends the abstract class while at the same time giving options to the child class to provide a certain amount of behaviour itself.

A Child Class extending the Abstract Class:

public class Child extends Parent {

public String getSon() {

return "Sons Name";

}

public String getDaughter(){

return "Daughters Name";

}

...

... //Code specific to the Child class

}

Answer 6

In general programming terms, a concrete class is one which can be instantiated, while an abstract class can only be instantiated via a fully implemented subclass.

Answer 7

Abstract classes are classes that can't be instantiated directly. In other words, you are meant to create subclasses, which you instantiate.