Getting this to move.

[Kelly Frasure]

I need this to move across the screen. Can anyone help?
This is an assignment for school, and I can't use any methods from the polygon class. I think I need to change the array values, but not quite sure how to go about it.
Here is the code:
import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
import javax.swing.Timer;
public class Truck1 extends Applet
{
private final int APPLET_WIDTH = 400;
private final int APPLET_HEIGHT = 400;
private final int DELAY = 20;
private Timer timer;
public int[] xStart = {15, 15, 15, 15, 15, 68, 70, 72, 75, 77,
80, 80, 80, 67, 64, 64, 64, 39, 19, 15};
public int[] yStart = {8, 70, 73, 75, 77, 77, 77, 77, 77, 77, 77,
55, 33, 33, 33, 20, 8, 8, 8, 8};
public int[] xMove = {20, 20, 20, 20, 20, 73, 75, 77, 80, 82,
85, 85, 85, 72, 69, 69, 69, 44, 24, 20};
public int[] yMove = {13, 75, 78, 80, 82, 82, 82, 82, 82, 82, 82,
60, 38, 38, 38, 25, 13, 13, 13, 13};
//===============================================================
public void init()
{
timer = new Timer (DELAY, new ReboundActionListener());
timer.start();
setBackground (Color.white);
setSize (APPLET_WIDTH, APPLET_HEIGHT);
}
//===============================================================
public void paint (Graphics page)
{
page.setColor (Color.red);
page.fillPolygon (xStart, yStart, xStart.length);
page.fillPolygon (xMove, yMove, xMove.length);
page.fillOval(25, 77, 25, 25); //left tire
page.fillOval(55, 77, 25, 25); //right tire
page.setColor(Color.white);
page.fillOval(30, 85, 10, 10); //center of left tire
page.fillOval(60, 85, 10, 10); //center of right tire
}
//=============================================================
private class ReboundActionListener implements ActionListener
{
public void actionPerformed (ActionEvent event)
{
repaint();
}
}
}

[Manfred Leonhardt]

Hi Kelly,
To make something move we need a point to move and all the other drawing points must be relative to it. See the following code. I started with your code and changed a few things.

import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
import javax.swing.Timer;
public class Truck1 extends Applet
{
  private final int APPLET_WIDTH = 400;
  private final int APPLET_HEIGHT = 400;
  private final int DELAY = 200;
  private final int STEPSIZE = 5;
  private Timer timer;
  private int[] xStart = new int[7];
  private int[] yStart = new int[7];
  private int[] xOffset = { 15, 15, 80, 80, 65, 65, 15 };
  private int[] yOffset = { 8, 77, 77, 33, 33, 8, 8 };
  private int xPos;
  private int yPos;
//===============================================================
  public void init()
  {
    timer = new Timer (DELAY, new ReboundActionListener());
    timer.start();
    setBackground (Color.white);
    xPos = 10;
    yPos = 10;
    adjustPosition();
  }
//===============================================================
  private void adjustPosition()
  {
    for( int i = 0; i < xStart.length; ++i )
    {
      xStart[i] = xOffset[i] + xPos;
      yStart[i] = yOffset[i] + yPos;
    }
  }
//===============================================================
  public void paint (Graphics page)
  {
    // Draw the truck body.
    page.setColor( Color.red );
    page.fillPolygon( xStart, yStart, xStart.length);
    //
    // Draw the tires.
    //
    int tireSize = 24;
    page.fillOval(xStart[0], yStart[1], tireSize, tireSize); //left tire
    page.fillOval(xStart[2]-tireSize, yStart[1], tireSize, tireSize ); //right tire
    //
    // Draw the tire centers
    //
    page.setColor(Color.white);
    int centerSize = tireSize / 2;
    int centerPt = centerSize / 2;
    page.fillOval( xStart[0]+centerPt, yStart[1]+centerPt, 
                   centerSize, centerSize ); //center of left tire
    page.fillOval( xStart[2]-tireSize+centerPt, yStart[1]+centerPt, 
                   centerSize, centerSize ); //center of right tire
    //
    // Adjust the elements to move.
    //
    for( int i = 0; i < xStart.length; ++i )
    {
      xPos += STEPSIZE;
      if( (xPos + 80) > APPLET_WIDTH )
      {
        xPos = 10;
        yPos += 80;
        if( (yPos + 77) > APPLET_HEIGHT )
        {
          yPos = 10;
        }
      }
    }
    adjustPosition();
  }
//=============================================================
  private class ReboundActionListener implements ActionListener
  {
    public void actionPerformed (ActionEvent event)
    {
      repaint();
    }
  }
}

Enjoy,
Manfred.