多线程之8锁问题

Phone 有两个方法：发送邮件和发送短信，每个方法都打印一句话，现在通过不同的方式对方法进行操作，回答出打印的先后顺序（建议先自己看代码认真思考，然后再看答案，文章结尾会对每个问题进行分析）

问题

1、标准访问，两线程中间睡眠 2 毫秒，先打印邮件还是短信？

class Phone {
    public synchronized void sendEmail() {
        System.out.println("send email");
    }
    public synchronized void sendSms() {
        System.out.println("send sms");
    }
}

public class Lock01 {
    public static void main(String[] args) throws InterruptedException {
        Phone phone = new Phone();
        new Thread(() -> phone.sendEmail(), "A").start();
        Thread.sleep(200);
        new Thread(() -> phone.sendSms(), "B").start();
    }
}

查看答案

send email
send sms

2、在 sendEmail() 方法中睡眠 4 秒，先打印邮件还是短信？

class Phone {
    public synchronized void sendEmail() {
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("send email");
    }
    public synchronized void sendSms() {
        System.out.println("send sms");
    }
}

public class Lock02 {
    public static void main(String[] args) throws InterruptedException {
        Phone phone = new Phone();
        new Thread(() -> phone.sendEmail(), "A").start();
        Thread.sleep(200);
        new Thread(() -> phone.sendSms(), "B").start();
    }
}

查看答案

send email
send sms

3、添加普通的 hello() 方法，先打印邮件还是 hello？

class Phone {
    public synchronized void sendEmail() {
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("send email");
    }
    public void hello() {
        System.out.println("hello");
    }
}
public class Lock03 {
    public static void main(String[] args) throws InterruptedException {
        Phone phone = new Phone();
        new Thread(() -> phone.sendEmail(), "A").start();
        Thread.sleep(200);
        new Thread(() -> phone.hello(), "B").start();
    }
}

查看答案

hello
send email

4、2 个手机，先打印邮件还是短信？

class Phone {
    public synchronized void sendEmail() {
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("send email");
    }

    public synchronized void sendSms() {
        System.out.println("send sms");
    }
}

public class Lock04 {
    public static void main(String[] args) throws InterruptedException {
        Phone phone1 = new Phone();
        Phone phone2 = new Phone();
        new Thread(() -> phone1.sendEmail(), "A").start();
        Thread.sleep(200);
        new Thread(() -> phone2.sendSms(), "B").start();
    }
}

查看答案

send sms
send email

5、2个静态同步方法，1部手机，先打印邮件还是短信？

class Phone {
    public static synchronized void sendEmail() {
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("send email");
    }

    public static synchronized void sendSms() {
        System.out.println("send sms");
    }
}

public class Lock05 {
    public static void main(String[] args) throws InterruptedException {
        Phone phone = new Phone();
        new Thread(() -> phone.sendEmail(), "A").start();
        Thread.sleep(200);
        new Thread(() -> phone.sendSms(), "B").start();
    }
}

查看答案

send email
send sms

**6、2个静态同步方法，2部手机，先打印邮件还是短信？**

class Phone {
    public static synchronized void sendEmail() {
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("send email");
    }

    public static synchronized void sendSms() {
        System.out.println("send sms");
    }
}

public class Lock06 {
    public static void main(String[] args) throws InterruptedException {
        Phone phone1 = new Phone();
        Phone phone2 = new Phone();
        new Thread(() -> phone1.sendEmail(), "A").start();
        Thread.sleep(200);
        new Thread(() -> phone2.sendSms(), "B").start();
    }
}

查看答案

send email
send sms

**7、1个静态同步方法，1个普通同步方法，1部手机，先打印邮件还是短信？**

class Phone {
    public static synchronized void sendEmail() {
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("send email");
    }

    public synchronized void sendSms() {
        System.out.println("send sms");
    }
}

public class Lock07 {
    public static void main(String[] args) throws InterruptedException {
        Phone phone = new Phone();
        new Thread(() -> phone.sendEmail(), "A").start();
        Thread.sleep(200);
        new Thread(() -> phone.sendSms(), "B").start();
    }
}

查看答案

send sms
send email

8、1个静态同步方法，1个普通同步方法，2部手机，先打印邮件还是短信？

class Phone {
    public static synchronized void sendEmail() {
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("send email");
    }

    public synchronized void sendSms() {
        System.out.println("send sms");
    }
}

public class Lock08 {
    public static void main(String[] args) throws InterruptedException {
        Phone phone1 = new Phone();
        Phone phone2 = new Phone();
        new Thread(() -> phone1.sendEmail(), "A").start();
        Thread.sleep(200);
        new Thread(() -> phone2.sendSms(), "B").start();
    }
}

查看答案

send sms
send email

分析