Thread: Moving sprite leaves a trail

Hi all, I am new to these forums and to Java programming so bare with me!

I am trying to create a simple checkers game for a mobile phone using Java. I have currently displayed the checker board and checkers. I want to use an on screen cursor to select the checker piece to move. I have displayed a cursor on the screen and I can move it.

However, it leaves a trail behind and I am struggling to work out what I need to do in order to fix this (even though I am pretty sure it is a matter of adding one or two lines!) My code is, as follows:

package CheckersBoard;
 
/**
 *
 * @author Chris
 */
 
import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.*;
import java.io.*;
 
 
 
public class CheckerBoard extends GameCanvas implements Runnable{
    private Display myDisplay;
    private long frameRate;
    private boolean sleeping;
    private Graphics g;
    private Sprite[] blackChecker;
    private Sprite[] whiteChecker;
    private Sprite cursor;
    private final int numberOfCheckers = 12;
 
    int row;                      // Row number, from 0 to 7
    int col;                      // Column number, from 0 to 7
    int x,y;                      // Top-left corner of square
    int z;                        //Used to store value of square dimensions
    int screenWidth = getWidth(); //Stores value of the screen width in px
    int screenHeight = getHeight();
    int curPositionX = getWidth()/2-20;
    int curPositionY = getHeight()/2-60;
 
    public CheckerBoard(Display d){
        super(true);
        myDisplay = d;
        frameRate = 40;
        g = this.getGraphics();
        whiteChecker = new Sprite[numberOfCheckers];
        blackChecker = new Sprite[numberOfCheckers];
    }
    public void start(){
        myDisplay.setCurrent(this);
        sleeping = false;
        if (screenWidth <= screenHeight) //Checks screen width is greater than screen height
            z = screenWidth/8;           //Divides screen width by 8
        else
            z = screenHeight/8;          //Divides screen height by 8
 
        for ( row = 0;  row < 8;  row++ ) {
             for ( col = 0;  col < 8;  col++) {
                x = col * z;                    //Set the square width to 1/8 of the screen width
                y = row * z;                    //Set the square height to 1/8 of the screen height
                if ( (row % 2) == (col % 2) ){   //Every other square
                   g.setColor(139,0,0);         //Colours the square red
 
                try{
                    Image black = Image.createImage("/res/blackChecker.png");
                    Image white = Image.createImage("/res/whiteChecker.png");
                    Image hand = Image.createImage("/res/cursor.PNG");
                    cursor = new Sprite(hand);
                    cursor.setPosition(curPositionX, curPositionY);
 
                    for (int i=0; i<numberOfCheckers; i++){
                        blackChecker[0] = new Sprite(black);
                        blackChecker[0].setPosition(30,0);
                        blackChecker[1] = new Sprite(black);
                        blackChecker[1].setPosition(90,0);
                        blackChecker[2] = new Sprite(black);
                        blackChecker[2].setPosition(150,0);
                        blackChecker[3] = new Sprite(black);
                        blackChecker[3].setPosition(210,0);
                        blackChecker[4] = new Sprite(black);
                        blackChecker[4].setPosition(0,30);
                        blackChecker[5] = new Sprite(black);
                        blackChecker[5].setPosition(60,30);
                        blackChecker[6] = new Sprite(black);
                        blackChecker[6].setPosition(120,30);
                        blackChecker[7] = new Sprite(black);
                        blackChecker[7].setPosition(180,30);
                        blackChecker[8] = new Sprite(black);
                        blackChecker[8].setPosition(30,60);
                        blackChecker[9] = new Sprite(black);
                        blackChecker[9].setPosition(90,60);
                        blackChecker[10] = new Sprite(black);
                        blackChecker[10].setPosition(150,60);
                        blackChecker[11] = new Sprite(black);
                        blackChecker[11].setPosition(210,60);
                        whiteChecker[0] = new Sprite(white);
                        whiteChecker[0].setPosition(0,210);
                        whiteChecker[1] = new Sprite(white);
                        whiteChecker[1].setPosition(60,210);
                        whiteChecker[2] = new Sprite(white);
                        whiteChecker[2].setPosition(120,210);
                        whiteChecker[3] = new Sprite(white);
                        whiteChecker[3].setPosition(180,210);
                        whiteChecker[4] = new Sprite(white);
                        whiteChecker[4].setPosition(30,180);
                        whiteChecker[5] = new Sprite(white);
                        whiteChecker[5].setPosition(90,180);
                        whiteChecker[6] = new Sprite(white);
                        whiteChecker[6].setPosition(150,180);
                        whiteChecker[7] = new Sprite(white);
                        whiteChecker[7].setPosition(210,180);
                        whiteChecker[8] = new Sprite(white);
                        whiteChecker[8].setPosition(0,150);
                        whiteChecker[9] = new Sprite(white);
                        whiteChecker[9].setPosition(60,150);
                        whiteChecker[10] = new Sprite(white);
                        whiteChecker[10].setPosition(120,150);
                        whiteChecker[11] = new Sprite(white);
                        whiteChecker[11].setPosition(180,150);
                        }
                }
                catch(IOException e){
                    System.err.println("Failed loading sprites" + e.getMessage());
                }
                }
                else                            //Every non red square
                   g.setColor(0,0,0);           //Colours the square black
                   g.fillRect(x, y, z, z);      //Draws the grid
             }
        Thread t = new Thread(this);
        t.start();
        }
    }
    public void stop(){
        }
    public void run(){
        while(!sleeping){
            updateGame();
            draw(g);
            try{
                Thread.sleep(frameRate);
               }
            catch(InterruptedException ie) {
                System.out.println(ie.getMessage());
               }
        }
}
    public void draw(Graphics g){
 
        for (int i=0; i<12; i++){
           blackChecker[i].paint(g);
           whiteChecker[i].paint(g);
        }
        flushGraphics();
        cursor.paint(g);
 
    }
    public void updateGame(){
        int keyState = this.getKeyStates();
        if ((keyState & LEFT_PRESSED) != 0)
                        {
            		curPositionX-=1;
                        cursor.setPosition(curPositionX,curPositionY);
 
                        }
        	if ((keyState & RIGHT_PRESSED) != 0)
                        {
            		curPositionX+=1;
                        cursor.setPosition(curPositionX,curPositionY);
                        }
        	if ((keyState & UP_PRESSED) != 0)
                        {
            		curPositionY-=1;
                        cursor.setPosition(curPositionX,curPositionY);
                        }
        	if ((keyState & DOWN_PRESSED) != 0)
                        {
            		curPositionY+=1;
                        cursor.setPosition(curPositionX,curPositionY);
                        }
       		checkBoundary(cursor);
 
    }
    public void checkBoundary(Sprite s) {
        	if (s.getX() < -s.getWidth())
            		s.setPosition(this.getWidth(),s.getY());
        	else if (s.getX() > this.getWidth())
            		s.setPosition(-s.getWidth(),s.getY());
                if (s.getY() < - s.getHeight())
            		s.setPosition(s.getX(), this.getHeight());
        	else if (s.getY() > this.getHeight())
            		s.setPosition(s.getX(), - s.getHeight());
    		}
}

Thanks in advance

Chris

I am sure you are right,

however, I wouldn't know how to delete the old sprite. Wouldn't deleting the sprite delete the entire thing off the screen or am I thinking wrong here?

Thanks for your help so far

How would I remove it from the screen? I'm really going round in circles with this now!

I solved it by using a png image as the board - Probably not the ideal way to do it but needs must!