以银行取款经典案例来演示线程冲突现象。 银行取钱的基本流程基本上可以分为如下几个步骤。
    （1）用户输入账户、密码，系统判断用户的账户、密码是否匹配。
    （2）用户输入取款金额
    （3）系统判断账户余额是否大于取款金额
    （4）如果余额大于取款金额，则取钱成功；如果余额小于取款金额，则取钱失败。 

    1. public class DrawMoneyDemo {
    2.     public static void main(String[] args) {
    3.         Account account=new Account("1234",1000);
    4.         new DrawMoney("老公",account,800).start();
    5.         new DrawMoney("老婆",account,800).start();
    6.     }
    7. }
    9. /**
    10.  * 账户类
    11.  */
    12. class Account{
    13.     //账号
    14.     private String accountNo;
    15.     //账户余额
    16.     private double balance;
    18.     public Account(){
    19.     }
    21.     public Account(String accountNo,double balance){
    22.         this.accountNo=accountNo;
    23.         this.balance=balance;
    24.     }
    26.     public String getAccountNo() {
    27.         return accountNo;
    28.     }
    30.     public void setAccountNo(String accountNo) {
    31.         this.accountNo = accountNo;
    32.     }
    34.     public double getBalance() {
    35.         return balance;
    36.     }
    38.     public void setBalance(double balance) {
    39.         this.balance = balance;
    40.     }
    41. }
    43. /**
    44.  * 取款线程
    45.  */
    46. class DrawMoney extends Thread{
    47.     //账号对象
    48.     private Account account;
    49.     //取款金额
    50.     private double drawMoney;
    51.     public DrawMoney(String name,Account account,double drawMoney){
    52.         super(name);
    53.         this.account=account;
    54.         this.drawMoney=drawMoney;
    55.     }
    57.     @Override
    58.     public void run() {
    59.         //判断当前账户余额是否大于或等于取款金额
    60.         if(this.account.getBalance()>=this.drawMoney){
    61.             System.out.println(this.getName()+"取钱成功！吐出钞票："+this.drawMoney);
    62.             try {
    63.                 Thread.sleep(1000);
    64.             } catch (InterruptedException e) {
    65.                 e.printStackTrace();
    66.             }
    67.             //更新账户余额
    68.             this.account.setBalance(this.account.getBalance()-this.drawMoney);
    69.             System.out.println("\t余额为："+this.account.getBalance());
    70.         }else{
    71.             System.out.println(this.getName()+"取钱失败，余额不足");
    72.         }
    73.     }
    74. }

    image.png
    结果明显不对，这就是线程不同步的后果