Moving a ball with arrow keys using Java Applet

Question

I am learning Java language and trying to make a simple maze game. I am able to draw a ball and the objects on the screen but I can't move the ball using arrow keys. Here is my code:

 import java.applet.*;
 import java.awt.*;
 import java.awt.event.KeyEvent;
 import javax.swing.*;
 import java.awt.event.*;
 import java.awt.Color;
 import java.awt.Dimension;
 import java.awt.Graphics;
 import java.awt.Graphics2D;
 import java.awt.RenderingHints;
 import java.awt.event.ActionEvent;
 import java.awt.event.KeyEvent;


public class game extends Applet implements ActionListener, KeyListener {
/**
 * 
 */
private static final long serialVersionUID = 1L;

double x = 0, y = 0;

static int MoveX = 210; 
static int MoveY = 800; 

 public void up(){
        MoveY = -2;
        MoveX = 0;
    }

    public void down(){
        MoveY = 2;
        MoveX = 0;
    }

    public void left(){
       MoveX = -2;
        MoveY = 0;
    }

    public void right(){
        MoveX = 2;
        MoveY = 0;
    }



public void paint(Graphics g){
    //g.drawLine(200+10,150-10, 200+190, 150-10);
    //g.drawLine(200+30,200-30, 200+190, 200-30);
    g.setColor(Color.BLUE);


    g.fillRect(200+10, 150-10, 200+40, 150-10);
    g.fillRect(300+40, 150-10, 300+70, 150-10);


    g.fillRect(200+10, 200-10, 200+10, 200-10);
    g.fillRect(200+10, 230-10, 200+10, 230-10);
    g.fillRect(200+10, 260-10, 200+10, 260-10);
    g.fillRect(200+10, 290-10, 200+10, 290-10);
    g.fillRect(200+10, 320-10, 200+10, 320-10);
    g.fillRect(200+10, 350-10, 200+10, 350-10);
    g.fillRect(200+10, 380-10, 200+10, 380-10);




    g.fillRect(600+300, 90-10, 100+100, 150-10);
    g.fillRect(600+300, 150-10, 100+100, 210-10);
    g.fillRect(600+300, 210-10, 100+100, 270-10);
    g.fillRect(600+300, 270-10, 100+100, 330-10);


    g.fillRect(600+100,400, 200, 180);
    g.fillRect(600+30,400, 200, 180);


    g.fillRect(1000+300, 90-10, 100+100, 150-10);
    g.fillRect(1000+300, 150-10, 100+100, 210-10);
    g.fillRect(1000+300, 210-10, 100+100, 270-10);
    g.fillRect(1000+300, 270-10, 100+100, 330-10);
    g.fillRect(1000+300, 330-10, 100+100, 390-10);
    g.fillRect(1000+300, 390-10, 100+100, 350-10);

    g.setColor(Color.RED); 
    int size =90;
    g.fillOval(MoveX, MoveY, size, size); 






}
public void keyPressed(KeyEvent e) {
    // TODO Auto-generated method stub
     int code = e.getKeyCode();

        if (code == KeyEvent.VK_UP){
            up();
        }

        if (code == KeyEvent.VK_DOWN){
            down();
        }

        if (code == KeyEvent.VK_LEFT){
            left();
        }

        if (code == KeyEvent.VK_RIGHT){
            right();
        }

}
public void keyReleased(KeyEvent e) {
    // TODO Auto-generated method stub

    int code = e.getKeyCode();

    if (code == KeyEvent.VK_UP){
        MoveY = 0;
    }
    if (code == KeyEvent.VK_DOWN){
        MoveY = 0;
    }
    if (code == KeyEvent.VK_LEFT){
        MoveX = 0;
    }
    if (code == KeyEvent.VK_RIGHT){
        MoveX = 0;
    }

}
public void keyTyped(KeyEvent e) {
    // TODO Auto-generated method stub

}
public void actionPerformed(ActionEvent e) {
    // TODO Auto-generated method stub
     repaint();
        x += MoveX;
        y += MoveY;

        if(x<0){
            MoveX = 0;
            x = 0;
        }

        if(x>750){
            MoveX = 0;
            x = 750;
        }

        if(y<0);{
            MoveY = 0;
            y = 0;
        }

        if(y>550){
            MoveY = 0;
            y = 550;
        }
   }


  }

Applet started successfully and the objects drawn. I pressed arrow keys but the ball did not move. How can I trigger the KeyListener methods?

Thank you so much!

1) Why code an applet? If it is due to the teacher specifying it, please refer them to [Why CS teachers should **stop** teaching Java applets](http://programmers.blogoverflow.com/2013/05/why-cs-teachers-should-stop-teaching-java-applets/). 2) See [Java Plugin support deprecated](http://www.gizmodo.com.au/2016/01/rest-in-hell-java-plug-in/) and [Moving to a Plugin-Free Web](https://blogs.oracle.com/java-platform-group/moving-to-a-plugin-free-web). 3) Why use AWT? .. — Andrew Thompson, May 02 '18 at 13:10
.. See [this answer](http://stackoverflow.com/questions/6255106/java-gui-listeners-without-awt/6255978#6255978) for many good reasons to abandon AWT components in favor of Swing. — Andrew Thompson, May 02 '18 at 13:10
@AndrewThompson This is my homework. I am a Computer Engineering Student. Btw, I will send the link of the article to my Professor :) — teraRockstar, May 02 '18 at 18:31

score 1 · Answer 1 · answered May 01 '18 at 12:46

You need to set the key listener on your Applet instance:

public void init() {
    addKeyListener(this);
}

Nothing will happen though, because you are not repainting your Applet. After the user presses a key you will need to repaint:

repaint();

The logic for your up(), down(), etc. functions are also incorrect. When you call the up() function the ball's position will be set to 0,-2, when you call the down() function the ball's position will be set to 0,2. You should be adjusting the existing ball position, not setting it to fixed coordinates.

Note that an `Applet` is (by default) not focusable. It won't necessarily have the input focus even if it is **made** focusable. Both are necessary for an applet to receive key events. So this answer, **by itself,** will **not** fix the reported problem. — Andrew Thompson, May 02 '18 at 13:08

score 0 · Accepted Answer · answered May 02 '18 at 18:36

0

I've solved the problem. Here is the link of code:

Mini maze game

answered May 02 '18 at 18:36

teraRockstar

55
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Moving a ball with arrow keys using Java Applet

2 Answers2