Java-0026-Synchronized同步

2016.8.4

在进行多线程操作时，对一些数据不进行同步的话，可能会产生一些奇奇怪怪的结果，其中可能会有非常严重的后果。

账户类

class BankAccount{
    public double balance=1000;
}

丈夫存钱

class Husband extends Thread{
    BankAccount account;
    public Husband(BankAccount account){
        this.account=account;
    }
    public void run(){
        System.out.println("当前余额："+account.balance);
        try {
            Thread.sleep(50);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        account.balance=account.balance+200;
        System.out.println("充值后余额："+account.balance);
    }
}

妻子存钱

class Wife extends Thread{
    BankAccount account;
    public Wife(BankAccount account){
        this.account=account;
    }
    public void run(){
        System.out.println("当前余额："+account.balance);
        try {
            Thread.sleep(50);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        account.balance=account.balance+200;
        System.out.println("充值后余额："+account.balance);
    }
}

执行

    public static void main(String[] args){
        BankAccount account=new BankAccount();
        Husband husband = new Husband(account);
        Wife wife = new Wife(account);
        husband.start();
        wife.start();
    }

结果

搜狗截图20160804210535.png
搜狗截图20160804210647.png
搜狗截图20160804210630.png
搜狗截图20160804210601.png

其中第1和第3种情况很严重，存的钱都变少了。

---

现在我们将run方法修改，用synchronized拿到account对象锁

    public void run(){
        synchronized(account){
            System.out.println("当前余额："+account.balance);
            try {
                Thread.sleep(50);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            account.balance=account.balance+200;
            System.out.println("充值后余额："+account.balance);
        }
    }

再运行，就不会产生错误了

搜狗截图20160805114732.png