Question

I am having this odd issue, and I am not sure what is causing it. Some times the issue isn’t even there. From what I am guessing, is that this is a Java memory issue or some sort of threading issue.

I have a Ship and the ship shoots Bullets If I hold down the Space key the ship shoots the bullets. I have the bullets set to fire off every 200 milliseconds. Some times they shoot fine and move at the same speed! Other times, they shoot they move at different speeds. What could cause this?

package JGame.Actions;

import JGame.GameObject.GameObject;
import javax.swing.AbstractAction;

public class MoveAction extends Action implements Runnable{

    protected GameObject obj;
    protected int endX = 0, endY = 0;
    protected int moveAmount = 0;
    protected Thread thread;

    public void moveToY(GameObject obj, int y, int amount, AbstractAction complete){
        this.obj = obj;
        this.endY = y;
        this.moveAmount = amount;
        this.complete = complete;
        thread = new Thread(this);
        thread.start();
    }

    public void run(){
        try{
            boolean run = true;
            while(run){
                int objY = obj.getY();
                if(objY > this.endY){
                    obj.setY(obj.getY() - 1);
                }else if(objY < this.endY){
                    obj.setY(obj.getY() + 1);
                }else{
                    run = false;
                    this.actionComplete();
                }
                thread.sleep(moveAmount);
            }
        }catch(Exception e){
        }
    }
}

Action Complete:

package JGame.Actions;

import javax.swing.AbstractAction;

public class Action {
    protected boolean actionComplete = false;
    protected AbstractAction complete;

    public void actionComplete(){
        complete.actionPerformed(null);
    }
}

In my code I call moveToY it is a very simple call but sometime the Bullets move at different speeds (wrong), and others they move at the same speed (right). I don’t know if it would help to mention that as the bullets move sometimes they slow down for a second or two then speed back up to the correct speed.

Edit: Main Thread

The following is my main thread with the paintComponent

@Override
public void run(){
    try{
        while(true){
            // Check for key press events
            Iterator actions = KeyboardMap.map.entrySet().iterator();
            while(actions.hasNext()){
                Map.Entry ap = (Map.Entry)actions.next();
                Mapping mp = (Mapping)ap.getValue();
                if(mp.pressed){
                    mp.run();
                }
            }

            // Check for click mouse events
            Iterator actions2 = MouseMap.map.entrySet().iterator();
            while(actions2.hasNext()){
                Map.Entry ap = (Map.Entry)actions2.next();
                Mapping mp = (Mapping)ap.getValue();
                if(mp.pressed){
                    mp.run();
                }
            }

            for(GameObject go : gameObjects){
                if(!go.getLeaveScreen()){
                    int goWidth = go.getWidth();
                    int goHeight = go.getHeight();
                    int goX = go.getX();
                    int goY = go.getY();
                    int gameWidth = Game.width;
                    int gameHeight = Game.height;
                    if(goX + goWidth >= gameWidth){
                        go.setX(gameWidth - goWidth);
                    }
                    if(goX <= 0){
                        go.setX(0);
                    }
                    if(goY + goHeight >= gameHeight){
                        go.setY(gameHeight - goHeight);
                    }
                    if(goY <= 0){
                        go.setY(0);
                    }
                }
            }
            this.repaint();
            Thread.sleep(roomSpeed);
        }
    }catch(Exception e){
    }
}

public void paintComponent(Graphics g){
    try{
        g.drawImage(bg, 0, 0, this);
        for(int i = 0; i < gameObjects.size(); i++){
            GameObject go = gameObjects.get(i);
            g.drawImage(go.getSprite(), go.getX(), go.getY(), this);
        }
    }catch(Exception e){
    }
}

Answer 1

Well, I guess you have a large number of concurrent threads running (one by moving bullet), and you expect each thread to wake up after exactly moveAmount milliseconds. You can’t have such a guarantee, because the thread scheduler allows each thread to run for some time one at a time, and you might thus have glitches.

Another problem is that you seem to execute modification on Swing components out of the event dispatch thread, which is clearly forbidden by Swing’s threading policy.