Question

Describe how you would develop object-oriented features of Java for the Quiz program developed in the Programming Assignments. In particular, describe how the program could use each of the following: class variables, instance variables, inheritance, polymorphism, abstract classes, "this", "super", interfaces, and event listeners.

Answer 1

Answer : Given data

* I have used following for the solution:

1. Calculator is a class:
2. which is abstact
3. which is having abstract method
4. which will define static methods for the polymorphism
5. MainCall is another class:
6. demonstarte super call from Calculator class
7. which will extends the Calculator to demonstarte inheritance
8. which will implement th InterfaceForDemo to demonstarte interface
9. InterfaceForDemo is interface to demonstarte interafce
10. contain a variable and method that are called by MainCall class
11. EventListenerDemo is a class to demonstarte EventListener

Explanation:

CALCULATOR CLASS CODE:

package demo1;

abstract class Calculator {

     

  //Class variable

  static String batch = "CE";

  

  //Instance variable

  int z;

    

  //Abstract method definition

  //Abstract method has no body

  abstract void abc();

  

  //Defining a method in abstract classes

  void xyz()

  {

  System.out.println("\nI am demonstrating ABSTRACT class");

  }

  

  public Calculator() {

     System.out.println("I am demonstrating SUPER call from Calculator class");

  }

     

  public void addition(int x, int y) {

     System.out.println("\nHere z is demonstarting THIS");

     this.z = x + y;

     System.out.println("\nSum is: " +z);

  }

     

  public void Subtraction(int x, int y) {

  this.z = x - y;

  System.out.println("\nDifference is: "+z);

  }

    

  //The Product will demonstrate the POLYMORPHISM

  // Method with 2 int parameter

  static int Product(int a, int b)

  {

  return a * b;

  }

  

  // Method with the same name but 2 double parameter

  static double Product(double a, double b)

  {

  return a * b;

  }

}

MAINCALL CLASS CODE:

package demo1;

//Here MainCall is inheriting Calculator and implementing InterfaceForDemo

public class MainCall extends Calculator implements InterfaceForDemo {

  

  //Abstract Class

  void abc() {

  System.out.println("\nI am implementing from ABSTRACT class");

  }

    

  //Super constructor call

     public MainCall() {

        super();

        System.out.println("\nI am inside maincall class \n\nCalling SUPER constructor from Calculator class");

     }

     

    public void multiplication(int x, int y) {

     this.z = x * y;

     System.out.println("\nProduct is: "+z);

     }

    

     //Method from interface

     public void display() {

        System.out.println("\nI am a method from INTERFACE\n");

     }

     

     //Main method

     public static void main(String args[]) {

        

     int a = 20, b = 10;

     //Creating an object for the class

     MainCall demo = new MainCall();

     

     //Printing class variable

     System.out.println("\nI am demonstrating CLASS VARIABLE: " + batch);

     

     //Super is executing these function call from Calculator class

     demo.addition(a, b);

     demo.Subtraction(a, b);

     demo.multiplication(a, b);

     

     //Method from abstract class implemented

     demo.xyz();

     demo.abc();

     

     //Final string value and Method from Interface called here

     System.out.println("\nI am final string value from INTERFACE: "+ value);

     demo.display();

     

     //Polymorphism methods called here from Calculator class

     //These methods are called by using CLASS NAME

     System.out.println("I am demonstrating POLYMORPHISM: ");

     System.out.println(Calculator.Product(3, 4));

     System.out.println(Calculator.Product(3.0, 4.3));

       

     }

     

}

INTERFACEFORDEMO INTERAFCE CODE:

package demo1;

public interface InterfaceForDemo {

  

  //Variable and method declaration in Interface

  final String value = "I am final value in interface";

void display();

  

}

EVENTLISTENERDEMO CLASS CODE:

package demo1;

import java.awt.*;

import java.awt.event.*;

class EventListenerDemo extends Frame implements ActionListener{

     TextField textField;

     EventListenerDemo(){

     

     //create components

     textField=new TextField();

     textField.setBounds(60,50,170,20);

     

     Button b=new Button("Click here!!");

     b.setBounds(100,120,80,30);

     

     //register listener

     b.addActionListener(this);//passing current instance

     

     //add components and set size, layout and visibility

     add(b);add(textField);

     setSize(300,300);

     setLayout(null);

     setVisible(true);

  }

     

  public void actionPerformed(ActionEvent e){

     textField.setText("Got Event Listener ");

  }

  public static void main(String args[]){

     new EventListenerDemo();

  }

}

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