第一篇随笔 写下 Java synchronized

Todo

1. 对比下 有无 synchronized的 运行结果， 就会发现 不同的线程 同时修改 同一个对象的某条属性 就会导致错乱。 因为某些线程修改的结果被覆盖了。

所以我们要加上 synchronized 来保证 互斥访问

```

class Account {

    private String name;
    private float amount;

    public Account(String name, float amount) {
        this.name = name;
        this.amount = amount;
    }

    public String getName() {
        return name;
    }

    public float getBalance() {
        return amount;
    }

    public void deposit(float amt) {
        float temp = amount;
        temp -= amt;

        try {
            //模拟其它处理所需要的时间，比如刷新数据库等
            Thread.sleep((int) (Math.random() * 10));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        amount = temp;
    }

    public void withdraw(float amt) {
        float temp = amount;
        temp += amt;

        try {
            Thread.sleep((int) (Math.random() * 10));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        amount = temp;
    }


}

public class Bank {
    private static int NUM_OF_THREAD = 1000;
    static Thread[] threads = new Thread[NUM_OF_THREAD];

    public static void main(String[] args) {
        Account acc = new Account("Francis", 1000.0f);

        for (int i = 0; i < NUM_OF_THREAD; i++) {
            threads[i] = new Thread(new Runnable() {
                @Override
                public void run() {
                    acc.deposit(100.0f);
                    acc.withdraw(100.0f);
                }
            });
            threads[i].start();
        }

        for (int i = 0; i < NUM_OF_THREAD; i++) {
            try {
                // 等待 所有线程运行结束
                threads[i].join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(String.format("Finally, %s's balance is: %f", acc.getName(), acc.getBalance()));
    }
}
```

```

class Account {

    private String name;
    private float amount;

    public Account(String name, float amount) {
        this.name = name;
        this.amount = amount;
    }

    public String getName() {
        return name;
    }

    public float getBalance() {
        return amount;
    }

    public synchronized void deposit(float amt) {
        float temp = amount;
        temp -= amt;

        try {
            //模拟其它处理所需要的时间，比如刷新数据库等
            Thread.sleep((int) (Math.random() * 10));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        amount = temp;
    }

    public synchronized void withdraw(float amt) {
        float temp = amount;
        temp += amt;

        try {
            Thread.sleep((int) (Math.random() * 10));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        amount = temp;
    }


}

public class Bank {
    private static int NUM_OF_THREAD = 1000;
    static Thread[] threads = new Thread[NUM_OF_THREAD];

    public static void main(String[] args) {
        Account acc = new Account("Francis", 1000.0f);

        for (int i = 0; i < NUM_OF_THREAD; i++) {
            threads[i] = new Thread(new Runnable() {
                @Override
                public void run() {
                    acc.deposit(100.0f);
                    acc.withdraw(100.0f);
                }
            });
            threads[i].start();
        }

        for (int i = 0; i < NUM_OF_THREAD; i++) {
            try {
                // 等待 所有线程运行结束
                threads[i].join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(String.format("Finally, %s's balance is: %f", acc.getName(), acc.getBalance()));
    }
}

```