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--);    }}