Thread: help i cant get my code working

I am very new to java and i have only been using it for a few days however after watching a tutorial on youtube i am having problems getting my circle (my player) to move using the arrow keys,when I run the game there aren't any errors but my player wont move.

This is my code:



game.java (what I run the game on)

import java.awt.Graphics;
 
 
public class game extends gameloop {
 
	public void init() {
		setSize(854,480);
		Thread th = new Thread(this);
		th.start();
		addKeyListener(this);
	}
 
	public void paint(Graphics g){
		g.fillRect(x, y, 20, 20);
	}
}

gameloop.java

import java.applet.Applet;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
 
 
public class gameloop extends Applet implements Runnable, KeyListener {
 
	public int x, y;
	public boolean up, down, left, right;
 
	public void run() {
 
		x = 400;
		y = 220;
 
		while(true){
 
			if (left) {
				x-=2;
				left = false;
			}
			if (up) {
				y-=2;
				up = false;
			}
			if (right) {
				x+=2;
				right = false;
			}
			if (down) {
				y+=2;
				down = false;
			}
			repaint();
			try {
				Thread.sleep(20);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
 
	}
 
	public void keyPressed(KeyEvent e) {
		if (e.getKeyCode() == 37) {
			left = true; 
		}  
		if (e.getKeyCode() == 38) {
			up = false;
		}
		if (e.getKeyCode() == 39) {
			right = false;
		}
		if (e.getKeyCode() == 40) {
			down = false;
		}
 
	}
 
	public void keyReleased(KeyEvent e) {}
 
 
 
	public void keyTyped(KeyEvent e) {}
 
}

can someone please tell me what i have done wrong, i would really appreciate it.

What you did wrong (or could do to improve your code and this post):

1. Post your code in code tags.
2. Post any errors you're getting when compiling or running your code. If none, say so.
3. Follow Java naming conventions: Class names are capitalized, methods and variables begin with lower-case and are camel-cased thereafter.
4. Indent your code correctly (may have been lost due to lack of code tags).
5. Style: if ( left == true ) is unnecessary. Simply if ( left ) will do.
6. Finally (for now), empty the keyReleased() method and change your run() method to something like:

    public void run()
    {
        x = 40;
        y = 40;
 
        while(true)
        {
            if (left)   
            {
                x -= 2;
                repaint();
                left = false;
            }
 
            // etc. . . . . .

I have updated my code the way you have said and edited it into my first post but it still doesn't work.

Originally Posted by alexrox27

there aren't any errors but my player wont move

Use printlns to verify what the code is actually doing.
print the key code in the key pressed event...
Inside the while(true) loop, print out the values of up, down, left, and right to see if they are updated in the loop.

Finding out what the code is doing will put you on the path to making it do what you want it to do

You should be using KeyEvent.VK_LEFT instead of 37... and the others

i have been testing what is and isn't working, my boolean variables have been working and have been moving my player when i manually set them how ever i have found that it is the println code to check it, i will try using the KeyEvent.VK_LEFT code and see if that works.

--- Update ---

I have just tested the game using this code

if (e.getKeyCode() == KeyEvent.VK_LEFT) {
			left = true; 
}

and it still doesn't work, thanks for the suggestion though.

Post your updated code. I made the changes I suggested to your code, and "it" works fine.

We can't help with "it isn't working" if we don't know what "it" is and what "working" means. Make an effort and I'll post my code.

my updated code is in my first post, can you please send me your version of the code because mine isnt working still

Hey man whats up. I took a second to go through your code and discovered several minor problems you might have overlooked.

First off when reading input from KeyEvent you should always use

if (e.getKeyCode() == KeyEvent.VK_#) {
//whatever you wanna do
}

Where the '#' would be the name of the key you are looking for input from.
Next, if you look here in your keyPressed method, as soon as the input is detected it is setting most your boolean values to false...

public void keyPressed(KeyEvent e) {
		if (e.getKeyCode() == 37) {
			left = true; 
		}  
		if (e.getKeyCode() == 38) {
			up = false;
		}
		if (e.getKeyCode() == 39) {
			right = false;
		}
		if (e.getKeyCode() == 40) {
			down = false;
		}
 
	}

When you have specified to only move the player when these values are true, like below. So you must change them all to true.

while(true){
 
			if (left) {
				x-=2;
				left = false;
			}
			if (up) {
				y-=2;
				up = false;
			}
			if (right) {
				x+=2;
				right = false;
			}
			if (down) {
				y+=2;
				down = false;
			}

Instead of setting up, down, left, and right to false when they are found true, you should set them false when the same key you pressed to move the player, is released. You can do this easily by copying and pasting your keyPressed method, changing "keyPressed" to "keyReleased", and replacing all the true values with false, like so:

	public void keyReleased(KeyEvent e) {
		if (e.getKeyCode() == KeyEvent.VK_LEFT) {
			left = false; 
		}  
		if (e.getKeyCode() == KeyEvent.VK_UP) {
			up = false;
		}
		if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
			right = false;
		}
		if (e.getKeyCode() == KeyEvent.VK_DOWN) {
			down = false;
		}
	}

This will make it so your player is moving only when the key used to move the player is held down.

What I have done in my code is the following:

• Changed the keyPressed method to read input by using "KeyEvent.VK_#"
• Set my boolean values to false in the keyReleased method
• Removed setting my boolean values to false, when they are found true in the while loop

GameLoop.java

import java.applet.Applet;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
 
 
public class GameLoop extends Applet implements Runnable, KeyListener {
 
	public int x, y;
	public boolean up, down, left, right;
 
	public void run() {
 
		x = 50;
		y = 50;
 
		while(true) {
			if(left) {
				x -= 2;
			}
			if(up) {
				y -= 2;
			}
			if(right) {
				x += 2;
			}
			if(down) {
				y += 2;
			}
			repaint();
			try {
				Thread.sleep(20);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
 
	}
 
	public void keyPressed(KeyEvent e) {
		if (e.getKeyCode() == KeyEvent.VK_LEFT) {
			left = true; 
		}  
		if (e.getKeyCode() == KeyEvent.VK_UP) {
			up = true;
		}
		if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
			right = true;
		}
		if (e.getKeyCode() == KeyEvent.VK_DOWN) {
			down = true;
		}
	}
 
	public void keyReleased(KeyEvent e) {
		if (e.getKeyCode() == KeyEvent.VK_LEFT) {
			left = false; 
		}  
		if (e.getKeyCode() == KeyEvent.VK_UP) {
			up = false;
		}
		if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
			right = false;
		}
		if (e.getKeyCode() == KeyEvent.VK_DOWN) {
			down = false;
		}
	}
 
	public void keyTyped(KeyEvent e) {};
 
}

Game.java

import java.awt.Graphics;
 
 
public class Game extends GameLoop {
 
	public void init(){
		setSize(300, 300);
		Thread th = new Thread(this);
		th.start();
		addKeyListener(this);
	}
 
	public void paint(Graphics g){
		g.fillRect(x, y, 20, 20);
	}
}

You should be able to use this information to make the player do most things you want with basic keyboard input Let me know if you have any questions or need further explanation.