Thread.sleep()延迟整个程序,而不仅仅是它之后的程序

Question

相当多的标题.代码应该绘制一个框,等待1秒,然后在不同的位置绘制一个新的框并重新绘制.相反,它会等待1秒然后画两个盒子.感谢您的帮助,如果我搞砸了格式化就很抱歉.

import javax.swing.*;
import java.awt.*;

public class GameRunner extends JPanel{
   @Override
   public void paintComponent (Graphics g){
      int x = 0;
      boolean directionRight = true;
      g.setColor(Color.blue);
      g.fillRect(300,400,100,100);
      repaint();
      try{
         Thread.sleep(1000);
      }
      catch (Exception ex){}
      g.fillRect(600,400,100,100);
      repaint();  
   }
   public static void main (String[] args){  
      JFrame frame = new JFrame("Submarine");
      GameRunner gameRunner = new GameRunner();
      frame.add(gameRunner);
      frame.setSize(1200,700);
      frame.setVisible(true);
      frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
   }
}

Answer 1

• Thread.sleep(1000); 将阻止当前运行的线程
• paintComponent 从Event Dispatching Thread的上下文中调用.
• 在完成处理当前(在本例中为"paint")事件之前,Swing不会更新UI的状态,这意味着当它被阻止时Thread.sleep,UI上不会更新任何内容,也不会处理任何新事件.

Swing是一个单线程框架.您永远不应该在Event Dispatching Thread的上下文中执行任何阻塞或长时间运行的操作.

查看Swing中的Concurrency以获取更多详细信息以及如何使用Swing Timers获得可能的解决方案.

作为旁注,如果UI或任何UI依赖于任何paint方法中的变量,则不应修改状态.绘画应该只绘制组件的当前状态,永远不要修改它,这包括repaint直接或间接调用

例如...

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class GameRunner extends JPanel {

    private int xPos = 300;

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.blue);
        g.fillRect(xPos, 400, 100, 100);
        repaint();
    }

    public GameRunner() {
        Timer timer = new Timer(1000, new ActionListener() {
            private boolean state = false;
            @Override
            public void actionPerformed(ActionEvent e) {
                if (state) {
                    xPos = 300;
                } else {
                    xPos = 600;
                }
                state = !state;
                repaint();
            }
        });
        timer.start();
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(700, 500);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new GameRunner());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}