package com.ninemax.application.multithread;public class FetchMoneyTest {		public static void main(String[] args) {				Bank bank = new Bank();		Thread t1 = new MoneyThread(bank);// 从银行取钱		Thread t2 = new MoneyThread(bank);// 从取款机取钱		t1.start();		t2.start();	}}class Bank {		private int money = 1000;	public synchronized int getMoney(int number) {		if (number < 0) {			return -1;		} else if (number > money) {			return -2;		} else if (money < 0) {			return -3;		} else {			try {				Thread.sleep(1000);			} catch (InterruptedException e) {				e.printStackTrace();			}			money -= number;			System.out.println("Left Money: " + money);						return number;		}	}}class MoneyThread extends Thread {		private Bank bank;	public MoneyThread(Bank bank) {		this.bank = bank;	}	@Override	public void run() {		System.out.println(bank.getMoney(800));	}}

运行结果:

Left Money: 200800-2

如果方法没有加synchronized关键字,运行结果:

Left Money: -600800Left Money: -600800

上面结果是因为在第一个线程sleep的时候,第二个线程也访问到了相同的资源,所以需要在方法上锁,才能同步.