java中，实现Runnable和继承Thread的区别

实现Runnable：

　　1、由于Java要求是单继承的，所以可以把这个继承的机会留给其他类， 

　　2、适合对共享性资源的访问 

下面通过例子说明：

　　卖票系统，有四个窗口同时进行

　　1、通过继承Thread类实现：  

　　

从结果可以看出，每个窗口卖得票种是不同的，不符合要求,下面我们来实现Runnable的方式来解决这种问题

　　2、通过实现Runnable接口

Thread-0 has tickets 100
Thread-1 has tickets 99
Thread-0 has tickets 98
Thread-0 has tickets 95
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Thread-3 has tickets 96
Thread-1 has tickets 97
Thread-1 has tickets 74
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Thread-3 has tickets 75
Thread-1 has tickets 71
Thread-2 has tickets 76
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Thread-0 has tickets 77
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Thread-0 has tickets 5
Thread-0 has tickets 4
Thread-0 has tickets 3
Thread-0 has tickets 2
Thread-0 has tickets 1
Thread-2 has tickets 54
Thread-1 has tickets 69
Thread-3 has tickets 70

可以看到，实现接口的方式基本满足要求，但是在实际项目过程中，对资源型的对象（火车票）的操作要排队，而且在整个操作过程中必须保持原子性！解决的办法

是把对资源性文件的操作放在synchronized的代码快中。下面这个例子中，是木有实现原子性导致的错误：

public class SellTickets {
    public static void main(String[] args) {
        /*
         new SellTicketsWindows().start();
         new SellTicketsWindows().start();
         new SellTicketsWindows().start();
         new SellTicketsWindows().start();
        */
        //从视频上看到的结果，这种办法可以达到四个窗口卖同一张票，为什么这里就不可以呢
        SellTicketsWindows tt = new SellTicketsWindows();
        new Thread(tt).start();
        new Thread(tt).start();
        new Thread(tt).start();
        new Thread(tt).start();
    }
}

class SellTicketsWindows implements Runnable {//extends Thread {
    int i = 100;
    String str = new String("");
    @Override
    public void run() {
        // TODO Auto-generated method stub
        
        while(true) {
            //synchronized(str) {
                if (i > 0) {
                    try{Thread.sleep(10);} catch(Exception e) {}//模拟进程调度程序强制未完成任务的线程进入就绪状态
                    System.out.println(Thread.currentThread().getName() 
                            + " has tickets " + i--);
                }else {
                    return ;
                }
            //}
        } 
    }
    
} 

Thread-1 has tickets 100
Thread-0 has tickets 100
Thread-2 has tickets 99
Thread-3 has tickets 98
Thread-0 has tickets 97
Thread-2 has tickets 96
Thread-3 has tickets 95
Thread-1 has tickets 94
Thread-0 has tickets 93
Thread-1 has tickets 92
Thread-3 has tickets 91
Thread-2 has tickets 90
Thread-0 has tickets 89
Thread-1 has tickets 88
Thread-3 has tickets 87
Thread-2 has tickets 86
Thread-0 has tickets 85
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Thread-3 has tickets 51
Thread-1 has tickets 50
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Thread-3 has tickets 35
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Thread-0 has tickets 32
Thread-1 has tickets 31
Thread-3 has tickets 30
Thread-2 has tickets 29
Thread-0 has tickets 28
Thread-3 has tickets 27
Thread-1 has tickets 26
Thread-2 has tickets 25
Thread-0 has tickets 24
Thread-3 has tickets 23
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Thread-3 has tickets 11
Thread-1 has tickets 11
Thread-2 has tickets 10
Thread-0 has tickets 9
Thread-3 has tickets 8
Thread-1 has tickets 7
Thread-2 has tickets 6
Thread-0 has tickets 5
Thread-1 has tickets 4
Thread-3 has tickets 3
Thread-2 has tickets 2
Thread-0 has tickets 1
Thread-3 has tickets 0
Thread-1 has tickets -1
Thread-2 has tickets -2

可以看到这种不符合现实的结果，导致这种情况的原因是，线程之间相互干扰，这就涉及到线程的安全性问题，

public class SellTickets {
    public static void main(String[] args) {
        /*
         new SellTicketsWindows().start();
         new SellTicketsWindows().start();
         new SellTicketsWindows().start();
         new SellTicketsWindows().start();
        */
        
        SellTicketsWindows tt = new SellTicketsWindows();
        new Thread(tt).start();
        new Thread(tt).start();
        new Thread(tt).start();
        new Thread(tt).start();
    }
}

class SellTicketsWindows implements Runnable {//extends Thread {
    int i = 100;
    String str = new String("");
    @Override
    public void run() {
        // TODO Auto-generated method stub
        
        while(true) {
            synchronized(str) {
                if (i > 0) {
                    try{Thread.sleep(10);} catch(Exception e) {}//模拟进程调度程序强制未完成任务的线程进入就绪状态
                    System.out.println(Thread.currentThread().getName() 
                            + " has tickets " + i--);
                }else {
                    return ;
                }
            }
        } 
    }
    
} 

Thread-0 has tickets 100
Thread-0 has tickets 99
Thread-0 has tickets 98
Thread-3 has tickets 97
Thread-3 has tickets 96
Thread-3 has tickets 95
Thread-1 has tickets 94
Thread-1 has tickets 93
Thread-1 has tickets 92
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Thread-1 has tickets 90
Thread-2 has tickets 89
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Thread-1 has tickets 83
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Thread-3 has tickets 76
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Thread-0 has tickets 72
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Thread-2 has tickets 54
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Thread-1 has tickets 51
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Thread-1 has tickets 47
Thread-3 has tickets 46
Thread-0 has tickets 45
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Thread-3 has tickets 43
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Thread-3 has tickets 40
Thread-1 has tickets 39
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Thread-1 has tickets 33
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Thread-3 has tickets 31
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Thread-0 has tickets 26
Thread-3 has tickets 25
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Thread-1 has tickets 21
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Thread-2 has tickets 19
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Thread-1 has tickets 14
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Thread-3 has tickets 11
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Thread-3 has tickets 9
Thread-0 has tickets 8
Thread-0 has tickets 7
Thread-0 has tickets 6
Thread-3 has tickets 5
Thread-3 has tickets 4
Thread-3 has tickets 3
Thread-1 has tickets 2
Thread-2 has tickets 1

这才是符合现实的结果！