Override a superclass's methods with a subclass

[zach&kody]

Hey everyone, I am part of a first year computer science class, and my friend and I are working on a project where we have to override a superclass's methods with a subclass. We have tried numerous techniques, but we have run out of ideas. Thanks in advance for all of your help. -From our computer to yours- zach&kody

[sunde887]

Here is a quick example.

class X{
  public void someMethod(){
    print 50 - 75
  }
}

class Y extends X{
  public void someMethod(){
    Print 25 - 50
  }
}

The method has the same name, but the subclass does something different. Read up on the tutorials on inheritance for more information.

[goldest]

Zach & Kody,

Go through this article which will give you more details about Overriding, Overloading, along with their rules and differences.

Here is the link : Method Overriding - Overloading

Hope that helps,

Goldest

[zach&kody]

This is the superclass that I am trying to override.

// This class represents a walker with two feet.

import java.awt.Image;
import java.awt.Graphics;
import javax.swing.JPanel;

public class Walker extends JPanel
{
  public static final int PIXELS_PER_INCH = 6;
  public Foot leftFoot, rightFoot;
  public int stepLength;
  public int stepsCount;

  // Constructor
  public Walker(int x, int y, Image leftPic, Image rightPic)
  {
    leftFoot =  new Foot(x, y - PIXELS_PER_INCH * 4, leftPic);
    rightFoot = new Foot(x, y + PIXELS_PER_INCH * 4, rightPic);
    stepLength = PIXELS_PER_INCH * 12;
  }

  // Returns the left foot
  public Foot getLeftFoot()
  {
    return leftFoot;
  }

  // Returns the right foot
  public Foot getRightFoot()
  {
    return rightFoot;
  }

  // Makes first step, starting with the left foot
  public void firstStep()
  {
    leftFoot.moveForward(stepLength);
    stepsCount = 1;
  }

  // Makes next step
  public void nextStep()
  {
    if (stepsCount % 2 == 0)  // if stepsCount is even
      leftFoot.moveForward(2 * stepLength);
    else
      rightFoot.moveForward(2 * stepLength);

    stepsCount++;  // increment by 1
  }

  // Stops this walker (brings its feet together)
  public void stop()
  {
    if (stepsCount % 2 == 0) // if stepsCount is even
      leftFoot.moveForward(stepLength);
    else
      rightFoot.moveForward(stepLength);

    stepsCount++;  // increment by 1
  }

  // Returns the distance walked
  public int distanceTraveled()
  {
    return stepsCount * stepLength;
  }

  // Draws this walker
  public void draw(Graphics g)
  {
    rightFoot.draw(g);
    leftFoot.draw(g);
  }
}

This is the subcass of which I am trying to override the superclass

// This class represents a subclass of Walker.

import java.awt.Image;
import java.awt.Graphics;

public class Bystander extends Walker
{
  public static final int PIXELS_PER_INCH = 6;
  private Foot lf, rf;
  private int stepLength;
  public int tapsCount;

  // Constructor
  public Bystander (int x, int y, Image leftPic, Image rightPic)
  {
    super(x, y, leftPic, rightPic);
    Foot lf = getLeftFoot();
    Foot rf = getRightFoot();
  }

  // Returns the left foot
  public Foot getLeftFoot()
  {
    return lf;
  }

  // Returns the right foot
  public Foot getRightFoot()
  {
    return rf;
  }

  // Makes first tap, starting with the left foot
  public void firstStep()
  {
    lf.turn(-45);
    tapsCount = 1;
  }

  // Makes next tap
  public void nextStep()
  {
    if (tapsCount % 2 == 0)  // if stepsCount is even
      lf.turn(45);
    else
      lf.turn(-45);

    tapsCount++;  // increment by 1
  }

  // Stops this walker (brings its feet together)
  public void stop()
  {
    if (tapsCount % 2 == 0) // if tapsCount is even
      lf.turn(45);
    else
      rf.turn(0);

    tapsCount++;  // increment by 1
  }

  // Returns the distance walked
  public int distanceTraveled()
  {
    return 0;
  }

  // Draws this walker
  public void draw(Graphics g)
  {
   super.draw(g);
  }
}

[dlorde]

When you inherit from a class by extending it, the subclass automatically gets all the superclass's variables and methods (with certain restrictions), so you don't need to duplicate all the same method code and variables in the subclass.

Only if you want the subclass to do something different to the superclass for some particular method, do you override that method by declaring it in the subclass and providing your own subclass implementation of it.

So the subclass should be empty apart from the methods where you want it to do something different to the superclass, and any extra variables it wants to add.

It would help in your example, if you explained what you want to achieve by overriding superclass methods.

[zach&kody]

The source Walker is supposed to walk the feet across the screen, and my objective is to override Walker with Bystander to make the feet stand still and tap back and forth.

[dlorde]

You don't override classes, you override methods - did you read the link goldest provided?

my objective is to ... make the feet stand still and tap back and forth

Have you considered changing the step methods to move forward and back instead of only moving forward? IOW overriding the step methods?

[zach&kody]

Thanks everyone! we have discovered the problem and we got the program to work, thanks for all of your help! -From our computer to yours'- zach&kody