同步方法解決執行緒安全問題

如果操作共享資料的程式碼完整的宣告在一個方法中，我們不妨將此方法宣告同步的。

同步方法的總結：
1．同步方法仍然涉及到同步監視器，只是不需要我們顯式的宣告。
2．非靜態的同步方法，同步監視器是:this
靜態的同步方法，同步監視器是:當前類本身

使用實現Runnable介面建立多執行緒

package com.klvchen.java;

class Window3 implements Runnable{
    private int ticket = 100;

    boolean isFlag = true;

    @Override
    public void
 
 run() {
        while (isFlag){
            show();

        }
    }

    private synchronized void show(){ //同步監視器：this
            if (ticket > 0){
                try {
                    Thread.sleep(100);
                }catch (InterruptedException e){
                    e.printStackTrace();
                }

                System.out.println(Thread.currentThread().getName() 
 
+ ":賣票,票號為:" + ticket);
                ticket--;
            }else {
                isFlag = false;
            }

    }
}
public class WindowTest3 {
    public static void main(String[] args) {
        Window3 w = new Window3();

        Thread t1 = new Thread(w);
        Thread t2 = new Thread(w);
        Thread t3 
 
= new Thread(w);

        t1.setName("執行緒1");
        t2.setName("執行緒2");
        t3.setName("執行緒3");

        t1.start();
        t2.start();
        t3.start();
    }
}

使用繼承Thread類建立多執行緒

package com.klvchen.java;

class Window4 extends Thread{

    private static int ticket = 100;

    private static boolean isFlag = true;

    @Override
    public void run() {
        while (isFlag){
            show();
        }
    }

    private static synchronized void show(){//同步監視器: Window4.class
        //private synchronized void show(){ //同步監視器: t1,t2,t3,此種解決方式不正確
        if (ticket > 0){
            try {
                Thread.sleep(100);
            }catch (InterruptedException e){
                e.printStackTrace();
            }

            System.out.println(Thread.currentThread().getName() + ": 賣票, 票號為: " + ticket);
            ticket--;
        }else {
            isFlag = false;
        }
    }
}

public class WindowTest4 {
    public static void main(String[] args) {
        Window4 t1 = new Window4();
        Window4 t2 = new Window4();
        Window4 t3 = new Window4();

        t1.setName("視窗1");
        t2.setName("視窗2");
        t3.setName("視窗3");

        t1.start();
        t2.start();
        t3.start();
    }
}