Why isn't the run method executed?

Question

I'm trying to create a square that can move by pressing keys. When I Compiled & Ran the code it wouldn't move. So I began debugging (as well as I'm capable of). The problem seems to be that the run() function isn't being called. Why is this ? My understanding was that when using the interface Runnable, the run method is called automatically. I posted all the code in action.

Why isn't run() being called automatically and how can I change my program so it will call ?

Game.java

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JFrame;
import javax.swing.JPanel;


public class Game extends JPanel implements Runnable{

private static final int WIDTH = 800, HEIGHT = WIDTH / 12 * 9; //Widescreen

private Thread game_thread;
private boolean running = false;
public int x_speed = 0, y_speed = 0;
public Square square;

public Game(){
    game_thread = new Thread("GameThread");
    square = new Square(this);

    addKeyListener(new KeyListener(){

        @Override
        public void keyPressed(KeyEvent e) {
            if(e.getKeyCode() == e.VK_A){
                x_speed = -1;
            }
            if(e.getKeyCode() == e.VK_D){
                x_speed = 1;
            }
            if(e.getKeyCode() == e.VK_S){
                y_speed = -1;
            }
            if(e.getKeyCode() == e.VK_W){
                y_speed = 1;
            }
        }

        @Override
        public void keyReleased(KeyEvent e) {

        }

        @Override
        public void keyTyped(KeyEvent e) {

        }

    });
}

public void start(){
    System.out.println("Started");
    game_thread.start();
    running = true;
    System.out.println(running);
}

public void stop(){
    try{
        running = false;
        game_thread.join();
    }catch(InterruptedException e){
        e.printStackTrace();
    }
}



public void paint(Graphics g){
    super.paint(g);

    Graphics2D g2d = (Graphics2D) g;

    g2d.setColor(Color.BLACK);
    g2d.fillRect(0, 0, WIDTH, HEIGHT);

    square.render(g2d);

}

public void update(){
    square.move();
    System.out.println(x_speed + ", " + y_speed);
}
public void run(){
    System.out.println("run method started");
    while(running){
        System.out.println("Running");
        //Update screen info
        update();

        //Re-render
        repaint();

        try{
            game_thread.sleep(10);
        }catch(InterruptedException e){
            e.printStackTrace();
        }

    }
}

public static void main(String args[]){
    JFrame frame = new JFrame("Moving Thangs");
    Game game = new Game();

    frame.setSize(game.WIDTH, game.HEIGHT);
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
    frame.setResizable(false);
    frame.add(game);
    frame.setVisible(true);
    game.start();
}
}

Square.java

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;


public class Square {

public static final int s_WIDTH = 80, s_HEIGHT = s_WIDTH;

public int x, y;

private Game game;

public Square(Game game){
    x = 50;
    y = 50;
    this.game = game;
}

public void move(){
    if(x >= 0 && x <= game.getWidth() - s_WIDTH){
        x += game.x_speed;
    }
    if(y >= 0 && y <= game.getHeight() - s_HEIGHT){
        y += game.y_speed;
    }
}

public void render(Graphics2D g2d){
    g2d.setColor(Color.ORANGE);
    g2d.fillRect(x, y, s_WIDTH, s_HEIGHT);
}

}

You forgot to pass the instance of `Game` to the `Thread`, so it defaults to its default behavior, which is doing nothing, use `new Thread(this, "GameThread")`. — Mark Rotteveel, May 18 '17 at 16:13
BTW: You should really swap `game_thread.start()` and `running = true` and make `running` volatile. — Mark Rotteveel, May 18 '17 at 16:16
Furthermore you failed to run the GUI from the Event Dispatch Thread (EDT, covered in official Tutorial, which I commend to your attention: http://docs.oracle.com/javase/tutorial/uiswing/index.html http://docs.oracle.com/javase/tutorial/uiswing/concurrency/dispatch.html. Also, study the Java coding conventions, especially the naming conventions. — Lew Bloch, May 18 '17 at 16:21
Please don't pass around the `this` reference to other classes from Game's constructor; your class is not fully constructed until the constructor completes. It might work fine most of the time, but you **will** run into unexpected behavior later on. Especially if threads are involved. — Daniel, May 19 '17 at 06:18
Your main thread ends immediately after starting the new `Game` thread. What's the point of creating the Game thread in that case? Why not just let the main thread do the work? — Solomon Slow, May 19 '17 at 15:41

score 1 · Answer 1 · answered May 18 '17 at 16:15

1

When you create the thread using new Thread("GameThread") you don't pass this as a runnable to the thread. You need to pass it as the first argument in the constructor like new Thread(this, "GameThread") and then everything should work.

answered May 18 '17 at 16:15

Vilsol

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Why isn't the run method executed?

1 Answers1