同步方法究竟做了什么？

Question

我正在使用Swing创建一个游戏.我制作start()并stop()同步,因为我被告知它更好.同步做什么以及使用它有什么好处？

我的代码:

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.image.BufferStrategy;
import java.awt.image.BufferedImage;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;

import javax.swing.JFrame;

public class SpritePractice extends Canvas implements Runnable{

private JFrame frame;
private final static int WIDTH = 200, HEIGHT = 200;
private final static int SCALE = 2;
private final static Dimension dimens= new Dimension(WIDTH*SCALE, HEIGHT*SCALE);
private BufferedImage image;
private Graphics g;
private long nanoSecond = 1000000000;
private double tick = nanoSecond/60;
private boolean running = false;
private int pixelsFromImage[];
private int pixel[][];
private static DateFormat dateFormat = new SimpleDateFormat("[" + "yyyy/MM/dd HH:mm:ss"
        +"]");
private static DateFormat dateFormat2 = new SimpleDateFormat("[" + "HH:mm:ss" + "]");

public SpritePractice()
{
    frame = new JFrame("Bomberman");
    frame.setSize(dimens);
    frame.setMinimumSize(dimens);
    frame.setMaximumSize(dimens);
    frame.setResizable(false);
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.add(this);
    frame.pack();
    frame.setVisible(true);
    init();
}
public void init()
{
    long startTime = System.nanoTime();
    Calendar cal = Calendar.getInstance();
    System.out.println("START: " + dateFormat.format(cal.getTime()));
    start();
}

public void run() 
{
    long now = System.nanoTime();
    long lastTick = System.nanoTime();
    long lastSecond = System.nanoTime();
    int frames = 0;

    while(running)
    {
        now = System.nanoTime();
        Calendar cal = Calendar.getInstance();

        if(now-lastTick >= tick)
        {
            lastTick = now;
            tick();
            render();
            frames++;
        }   
        if(now-lastSecond >= nanoSecond)
        {
            lastSecond = now;
            System.out.println(dateFormat2.format(cal.getTime()) + "FPS: " + frames);
            frames = 0;
        }
    }
}
public void tick()
{
    //updates values
}
public void render()
{
    BufferStrategy bs = getBufferStrategy();
    if(bs==null)
    {
        createBufferStrategy(2);
        return;
    }
    Graphics g = bs.getDrawGraphics();
    g.fillRect(0, 0, WIDTH*2, HEIGHT*2);
    g.dispose();
    bs.show();
    //renders graphics
}
public synchronized void start()
{
    running = true;
    run();
}
public synchronized void stop()
{
    running = false;
}
public static void main(String[] args)
{
    new SpritePractice();
}

}

Answer 1

进入synchronized方法的线程获取对拥有该方法的整个对象的锁定.

你的具体情况,你可以肯定的是不会有那个执行两个线程并发start()与stop()同步.

在此阅读有关同步方法的更多信

例如,如果一个线程进入该start()方法,它将在另一个线程进入该stop()方法之前完成其执行.如果不同步这两种方法,可以进行以下连续:

- 线程1进入start()
- 线程1设置布尔字段为true
- 线程2进入stop()
- 线程2设置boolean字段为false
- 线程1执行run()方法

你肯定不想要的.