java线程同步

/*
 同步的前题：
 1.必须要有两个或以上线程
 2.必须是多个线程使用一个锁

 优点：解决多线程安全问题
 弊端：多个线程判断锁，消耗资源

 */
package pack;
public class Main {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Ticket t = new Ticket();
        Thread t1 = new Thread(t);
        Thread t2 = new Thread(t);
        Thread t3 = new Thread(t);
        Thread t4 = new Thread(t);
        t1.start();
        t2.start();
        t3.start();
        t4.start(); 
    }

    public static void sys(Object obj) {
        System.out.println(obj);
    }

}

/*class Ticket implements Runnable {     //同步代码块
    Object obj = new Object();
    private int tick = 100;
    public void run() {
        while(true) {
            synchronized(obj) {
                if(tick>0)
                Main.sys(Thread.currentThread().getName()+"---"+tick--);
            }

        }
    }
}*/

class Ticket implements Runnable {     //同步函数
    Object obj = new Object();
    private int tick = 100;
    public void run() {
        while(true) {
            show();
            }   
        }

    public synchronized void show() {   
        if(tick>0)
            Main.sys(Thread.currentThread().getName()+"---"+tick--);
    }
}