synchronized关键字的使用

1.使用synchronized修饰代码块，使用语法如下：

public class Ticket implements Runnable{
    /**车票库存*/
    int tickets = 100;
    /**创建一个锁对象，这个对象有多个线程共同使用*/
    static Object obj = new Object();
    @Override
    public void run(){
        while (true){
            //多线程共享代码块
            synchronized (obj) {
                if (tickets > 0) {
                    System.out.println(Thread.currentThread().getName() + "窗口正在售卖第" + (tickets--) + "票");
                } else {
                    break;
                }
            }
        }
        System.out.println(Thread.currentThread().getName()+"窗口售完票");
    }
}

2.使用synchronized修饰对象方法，代码如下：

public class Ticket implements Runnable{
    /**车票库存*/
    int tickets = 100;
    @Override
    public void run(){
        while (true){
            if(isFinish()) {
                break;
            }
        }
        System.out.println(Thread.currentThread().getName()+"窗口售完票");
    }

    public synchronized boolean isFinish(){
        boolean isFinish = false;
        if (tickets > 0) {
            System.out.println(Thread.currentThread().getName() + "窗口正在售卖第" + (tickets--) + "票");
        } else {
            isFinish = true;
        }
        return isFinish;
    }

    public static void main(String args[]){
        Ticket ticket = new Ticket();
        Thread thread1 = new Thread(ticket,"窗口1");
        Thread thread2 = new Thread(ticket,"窗口2");
        Thread thread3 = new Thread(ticket,"窗口3");
        Thread thread4 = new Thread(ticket,"窗口4");

        thread1.start();
        thread2.start();
        thread3.start();
        thread4.start();
    }
}

　　需要注意的是，现在的锁对象为当前this的Ticket。

3.使用synchronized修饰类方法，代码如下：

public class Ticket extends Thread{
    private String name;

    public Ticket(String name){
        super(name);
        this.name = name;
    }

    /**车票库存*/
   static int tickets = 100;
    @Override
    public void run(){
        while (true){
            if(isFinish()) {
                break;
            }
        }
        System.out.println(Thread.currentThread().getName()+"窗口售完票");
    }

    public static synchronized boolean isFinish(){
        boolean isFinish = false;
        if (tickets > 0) {
            System.out.println(Thread.currentThread().getName() + "窗口正在售卖第" + (tickets--) + "票");
        } else {
            isFinish = true;
        }
        return isFinish;
    }

    public static void main(String args[]){
        Ticket ticket1 = new Ticket("窗口1");
        Ticket ticket2 = new Ticket("窗口2");
        Ticket ticket3 = new Ticket("窗口3");
        Ticket ticket4 = new Ticket("窗口4");

        ticket1.start();
        ticket2.start();
        ticket3.start();
        ticket4.start();
    }
}

　　*注意：synchronized中如果有sleep()方法，cup在休眠时期不会让出资源