Java – Abstract Classes

Abstraction:

• Abstraction is a concept of hiding implementations and shows required functionality.
• Abstraction describes “What an object can do instead how it does it?”

Abstract Class:

• Define a class with abstract keyword.
• Abstract class consists concrete methods and abstract methods.
  • Concrete Method: A Method with body.
  • Abstract Method: A Method without body.

Class	Abstract Class
Class allows only Concrete methods	Abstract Class contains Concrete and Abstract methods
class A {             void m1(){                         logic;             }             void m2(){                         logic;             } }	abstract class A {             void m1(){                         logic;             }             abstract void m2(); }

Note: We cannot instantiate (create object) to abstract class because it has undefined methods.

abstract class Demo {             void m1(){                         // logic             }             abstract void m2(); } class Main {             public static void main(String[] args){                         Demo obj = new Demo();  // Error:             } }

Extending Abstract class:

• Every abstract class need extension(child).
• Child override the abstract methods of Abstract class.
• Through Child object, we can access the functionality of Parent (Abstract).

abstract class Parent {             void m1()             {                         System.out.println(“Parent class concrete m1()”);             }             abstract void m2(); } class Child extends Parent {             void m2() // override             {                                   System.out.println(“Overridden m2() method of Abstract class”);             } } class Main {             public static void main(String args[])             {                         Child obj = new Child();                         obj.m1();                         obj.m2();             } }

Initializing abstract class instance variables:

• Abstract class can have instance variables.
• Using super(), we initialize Abstract class instance variables in Child object creation process.

import java.util.Scanner ; abstract class Parent {             String pname;             Parent(String pname)             {                         this.pname = pname ;             }             abstract void details(); } class Child extends Parent {             String cname ;             Child(String pname, String cname)             {                         super(pname);                         this.cname = cname ;             }             void details()             {                         System.out.println(“Parent Name is: “+super.pname);                         System.out.println(“Child Name is : “+this.cname);             } } class Main  {             public static void main(String[] args)             {                         Scanner scan = new Scanner(System.in);                         System.out.print(“Enter Parent Name : “);                         String pname = scan.next();                         System.out.print(“Enter Child Name : “);                         String cname = scan.next();                         Child obj = new Child(pname, cname);                         obj.details();             } }