inner classes in java

 Internal stuff of inner classes

internal stuff of inner classes,internal stuff in inner classes in java,what is inner class,how inner class works,how inner classs works with example
Inner Classes: inner class is a class written inside another class.use of inner class is to protect the data not available to others means providing security for the class at that time we go for inner classes

Example: Best example for the inner classes 

"Bank Account: providing the security for calculating intrest of the total amount deposited in bank"

Observe the following program:

import java.io.*;
class BankAct
{
    private double balance;
    BankAct(double b)
    {
        balance = b;
    }
   
    void contact(double r)throws IOException
    {
        int i=0;
        do{
            System.out.print("Enter password:");
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            String pwd = br.readLine();
           
            if(pwd.equals("naga123"))
            {
                Interest in = new Interest(r);
                in.calculateInterest();
                return; //or System.exit(0);
            }
            else
            {
                if(i==2)
                {
                    System.out.println("your accout has been blocked");
                    return;
                }
                else
                {
                    System.out.println("Sorry, you are not an authorized person");
                    i++;
                }
               
               
            }
        }while(i<=2);
       
    }
    private class Interest //this is an inner class reside in security area
    {
        private double rate;

        Interest(double r)
        {
            rate = r;
        }
        void calculateInterest()
        {
            double interest = balance*rate/100;
            balance +=interest;
            System.out.println("Updated Balance= "+balance);
        }
    }
}
class InnerClassBankActDemo
{
    public static void main(String[] args)throws IOException
    {
        BankAct act = new BankAct(10000);
        act.contact(9.5);
    }
}

important interview questions in java

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Abstract classes and Abstract methods

Abstract Class: Abstact class is a class which contains abstract methods as well as concrete(normal) methods we can not create an object for abstract classes.but we can create a reference for that


Abstract method: An Abstract method does not have method body it contains only  the method header

Example:
       
abstract class Myclass
{
    abstract void calculate(double x);
}
class Sub1 extends Myclass
{
    void calculate(double x)
    {
        System.out.println("square of "+x+" is "+(x*x));
    }
}
class Sub2 extends Myclass
{
    void calculate(double x)
    {
        System.out.println("squre root of "+x+" is "+Math.sqrt(x));
    }
}
class Sub3 extends Myclass
{
    void calculate(double x)
    {
        System.out.println("cube of "+x+" is "+(x*x*x));
    }
}
class Test
{
    public static void main(String[] args)
    {
        Sub1 obj1 = new Sub1();
        Sub2 obj2 = new Sub2();
        Sub3 obj3 = new Sub3();

      /* 2 ways to call calculate() method */

      /* 1.creating objects to subclasses of an abstarct class and call calculte()
           using that object reference*/

        //obj1.calculate(3);
        //obj2.calculate(4);
        //obj3.calculate(5);
       
      /*2.create a reference variable to Myclass once reference is created it can
          be used to refer to the objects of subclasses */
        Myclass ref;  //ref is the referance of myclass as this variable will not take any memory because of it is an abstract class ref
        ref = obj1; //ref is refering to obj1
        obj1.calculate(3);
        ref = obj2;//ref is refering to obj2
        obj2.calculate(4);
        ref = obj3;//ref is refering to obj3
        obj3.calculate(5);
    }
}

Output: Squre of 3.0 is 9.0
             Suare root of 4.0 is 2.0
             Cube of 5.0 is 125.0