Question

package com.Multiply.com;

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

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


public class Core extends JPanel {
public static void main(String[] args){
    Core game = new Core();

    game.frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    game.frame.setTitle("Multiply");
    game.frame.setIconImage(testIcon);
    game.frame.add(game);
    game.frame.pack();
    game.frame.setLocationRelativeTo(null);
    game.frame.setResizable(false);
    game.frame.setVisible(true);
    t1.start();

    running = true;
    Collision.charCollision();

}

//start of variables
private static final long serialVersionUID = 1L;
public static int width = 1280; //width and height of the screen
public static int height = 720;

public static boolean running = false;

public static int charX = width /2 - 50;
public static int charY = height /2 - 50;
public static int charSizeX = 50;
public static int charSizeY = 50;
public static double charSpeed = 10;

public static Image testIcon = Toolkit.getDefaultToolkit().getImage("Multiply_Icon.png"); //Icon variables, locates the icon in the folder

JFrame frame = new JFrame();    //the frame variable

static Thread t1 = new Thread();

public Core(){
    KeyListener listener = new MyKeyListener();
    addKeyListener(listener);
    setFocusable(true);

    Dimension size = new Dimension(width, height);  //variable that sets the size of the window to 1280x720p
    setPreferredSize(size);                         //Sets the size of the window to "size" 

    frame = new JFrame();                           //makes frame into the JFrame window
}

public class MyKeyListener implements KeyListener {
    @Override
    public void keyPressed(KeyEvent e) {
        int keyCode = e.getKeyCode();
        //System.out.println("keyPressed="+KeyEvent.getKeyText(e.getKeyCode()));
        if(keyCode == KeyEvent.VK_W){
            charY-= charSpeed;
            repaint();
        }
        else if(keyCode == KeyEvent.VK_A){
            charX-= charSpeed;;
            repaint();
        }
        else if(keyCode == KeyEvent.VK_S){
            charY+= charSpeed;
            repaint();
        }
        else if(keyCode == KeyEvent.VK_D){
            charX+= charSpeed;
            repaint();
        }   
    }
    @Override
    public void keyReleased(KeyEvent e) {
        int keyCode = e.getKeyCode();
        //System.out.println("keyReleased="+KeyEvent.getKeyText(e.getKeyCode()));
        if(keyCode == KeyEvent.VK_ESCAPE){
            ConfigFileWriter cfw = new ConfigFileWriter();
            if(cfw.wroteFile == false){
                cfw.openFile();
                cfw.writeFile();
                cfw.closeFile();
                cfw.wroteFile = true;
                System.out.println("wroteFile = true");
                }
            running = false;
            System.out.println("Escape");
            try {
                t1.join();
            } catch (InterruptedException e1) {
                e1.printStackTrace();
            }
            System.exit(0);
        }
        else if(keyCode == KeyEvent.VK_OPEN_BRACKET){   //To be removed, testing purposes
            charSpeed-= 1;
        }
        else if(keyCode == KeyEvent.VK_CLOSE_BRACKET){
            charSpeed+= 1;
        }
        else if(keyCode == KeyEvent.VK_L){
            ConfigFileReader cfr = new ConfigFileReader();

            cfr.openFile();
            cfr.readFile();
            cfr.closeFile();
            charSpeed = Double.parseDouble(cfr.speed);
        }
    }
    @Override
    public void keyTyped(KeyEvent e) {
        // TODO Auto-generated method stub

    }
}

public void paint(Graphics g) {     // Draws top first to bottom last 
    Graphics2D g2 = (Graphics2D) g;

    Image background = Toolkit.getDefaultToolkit().getImage("C:/Users/Kanin/Desktop/Multiply_Game_Engine/Images/Black_Background.png");
    Image character = Toolkit.getDefaultToolkit().getImage("C:/Users/Kanin/Desktop/Multiply_Game_Engine/Images/Character.png"); // C:/Users/Kanin/Desktop/Multiply_Game_Engine/ 
    g2.drawImage(background, 0, 0, this); //draws the black background
    g2.drawImage(character, charX, charY, charSizeX, charSizeY, this);
}

}

package com.Multiply.com;

public class Collision extends Core {
private static final long serialVersionUID = 1L;
public static void charCollision(){
    while(running){
        System.out.println("Running");  //Won't detect unless this is here for some reason.
        if(charX < -1){         //Character can't go past the left side of the screen.
            charX = 0;
        }
        else if(charX > 1240){  //Character can't go past the right side of the screen.
            charX = 1240;
        }
        else if(charY < -1){    //Character can't go above the top side of the screen.
            charY = 0;
        }
        else if(charY > 680){   //Character can't go below the bottom side of the screen.
            charY = 680;
        }
    }
}
}

在最顶端附近说的System.out.println（ “暗战”）; 如果我没有那条线，它就不会注册我的区块已超出界限而且它会继续下去。当我运行游戏时，如果我删除了system.out代码块，它甚至不会在if语句中运行任何东西

Answer 1

我的猜测是你注册的KeyListener是在与主线程（GUI框架产生的线程之一）不同的线程中执行的，但是Collision.charCollision方法是在主线程。当省略System.out.println语句时，方法charCollision中的变量假定为VM自包含，但只要您插入与控制台的交互（从而与其他线程交互））变量running与GUI线程保持同步。您可以尝试声明GUI中以及主线程中使用的所有变量volatile，看看是否已经解决了您的问题。有关多线程的详细信息，请参阅Loop doesn't see changed value without a print statement。

Java不需要的代码行，但我不知道为什么

1 个答案: