Java线程安全—synchronized

 1.同步代码块

继承Thread实现多线程，同步代码块实现线程安全

public class ThreadDemo2 extends  Thread {

    public ThreadDemo2(String name)
    { super(name);}
    private static int ticketNum = 100;// 共有100张门票

    @Override
    public void run() {
        while (true) {
            synchronized (ThreadDemo2.class) {
                if (ticketNum > 0) {
                    System.out.println(Thread.currentThread().getName() + "售卖的门票号：" + ticketNum);
                    try {
                        sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                    ticketNum--;
                }
            }
            if (ticketNum <= 0) {
                return;//为了减少synchronized 中代码，结束判断放在外部
            }
        }
    }



    public static void main(String[] args) {
        //所有的线程共用一个锁，因为都是通过一个Ticket 对象创建的线程，因此用this作为锁
        ThreadDemo2 t1 = new ThreadDemo2("窗口1");
        t1.start();
        ThreadDemo2 t2 = new ThreadDemo2("窗口2");
        t2.start();
        ThreadDemo2 t3 = new ThreadDemo2("窗口3");
        t3.start();
    }
}

 线程安全：方法二 同步方法

//示例： 售卖100张门票,实现多个窗口售卖
//线程安全synchronized ：同步代码块
// 1.实现Runna接口
public class ThreadDemo1 implements Runnable {

    private static int ticketNum = 100;// 共有100张门票

    @Override
    public void run() {
        while (true) {
            buyTicket();
        }
    }

    public synchronized void buyTicket()  {
        if (ticketNum > 0) {
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            System.out.println(Thread.currentThread().getName() + "售卖的门票号：" + ticketNum);
            ticketNum--;
        }
    }

    public static void main(String[] args) {
        //所有的线程共用一个锁，因为都是通过一个Ticket 对象创建的线程，因此用this作为锁
        ThreadDemo1 thread = new ThreadDemo1();

        Thread t2 = new Thread(thread);
        t2.setName("窗口2");
        t2.start();
        Thread t3 = new Thread(thread);
        t3.setName("窗口3");
        t3.start();
        Thread t1 = new Thread(thread);
        t1.setName("窗口1");
        t1.start();
    }
}

实现Runnable 接口，同步方法实现线程安全

/示例： 售卖100张门票,实现多个窗口售卖
//线程安全synchronized ：同步代码块
// 1.实现Runna接口
public class ThreadDemo2 extends  Thread {

    public ThreadDemo2(String name)
    { super(name);}
    private static int ticketNum = 100;// 共有100张门票

    @Override
    public void run() {
        while (true) {
            ThreadDemo2.buyTicket();
        }
    }
//    同步监视器是类：静态方法
    public synchronized static void buyTicket(){

            if (ticketNum > 0) {
                System.out.println(Thread.currentThread().getName() + "售卖的门票号：" + ticketNum);
                try {
                    sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                ticketNum--;
            }
    }





    public static void main(String[] args) {
        //所有的线程共用一个锁，因为都是通过一个Ticket 对象创建的线程，因此用this作为锁
        ThreadDemo2 t1 = new ThreadDemo2("窗口1");
        t1.start();
        ThreadDemo2 t2 = new ThreadDemo2("窗口2");
        t2.start();
        ThreadDemo2 t3 = new ThreadDemo2("窗口3");
        t3.start();

}}