CODEWITHSUNDEEP
javaappletawtkeylistener
Philippe
Philippe

Reputation: 670

Why doesn't the ball move around in my applet when I press a button?

I am very new to Java and programming in general, so I tried to write a simple program whose only job is to make a ball moving around with the arrow keys and jumping with the space button. The program compiles but the ball doesn't move.

I probably didn't fully understood the Applet principles, could you explain to me the mistake I made?

Applet:

package test_game;

import java.applet.Applet;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

public class Starting_Point extends Applet implements Runnable, KeyListener {

    private static final long serialVersionUID = 1L;
    private static final int WIDTH = 700;
    private static final int HEIGHT = 300;
    Character Phil;
    Thread thread;

    @Override
    public void init() {
        setSize(WIDTH,HEIGHT);
        Phil = new Character(50, 200);
    }

    @Override
    public void start() {
        thread = new Thread(this);
        thread.start();
    }

    public void run() {
        while (true) {
            repaint();  
        }
    }

    @Override
    public void paint(Graphics arg0) {
        Phil.paint(arg0);
    }

    @Override
    public void keyPressed(KeyEvent arg0) {
        switch (arg0.getKeyCode()) {
            case (KeyEvent.VK_LEFT): Phil.setX(Phil.getX() - Phil.getDx());
                break;
            case (KeyEvent.VK_RIGHT): Phil.setX(Phil.getX() + Phil.getDx());
                break;
            case (KeyEvent.VK_SPACE): Phil.setDy(Character.gravity * Character.dt);
                Phil.setY(Phil.getY() + .5*Character.gravity*Character.dt*Character.dt + Phil.getDy()*Character.dt + Character.jump);
                break;
        }
    }

    @Override
    public void keyReleased(KeyEvent arg0) {
        // TODO Auto-generated method stub
    }

    @Override
    public void keyTyped(KeyEvent arg0) {
        // TODO Auto-generated method stub
    }
}

Character class:

package test_game;

import java.awt.Color;
import java.awt.Graphics;

public class Character {

    private int x;
    private int y;
    private int radius = 10;
    Graphics g;
    public static final int gravity = 15;
    private static final double dx = 4;
    public double dy;
    public static final double dt = .2;
    public static final int jump = 30;

    public Character(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public void setX(double d) {
        this.x = (int) d;
    }

    public void setY(double d) {
        this.y = (int) d;
    }

    public double getDx() {
        return dx;
    }

    public int getX() {
        return x;
    }

    public int getY() {
        return y;
    }

    public void setDy(double dy) {
        this.dy = dy;
    }

    public double getDy() {
        return dy;
    }

    public void paint(Graphics g) {
        g.setColor(Color.black);
        g.fillOval(x, y, radius, radius);   
    }
}

Upvotes: 0

Views: 268

Answers (1)

Ferrybig
Ferrybig

Reputation: 18824

You have defined a KeyListener inside you code. However, you forgot to register this event listener to a component, so its never called.

How to register your KeyListener:

Place the following code inside your start():

this.addKeyListener(this);

This fixes the problem with the character from moving to the left or right, however the jumping isn't fixed, fixing the jumping requires more code that calculates the correct y+ that you require, the current code always add 0 (rounded to 0 using the (int) you use) to the y coordinate when you press space.

Upvotes: 1

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