秒懂JAVA线程锁

问题1：先打印sms还是call？ 答案：先sms,因为synchronized锁是锁对象的，谁先拿到锁谁就先执行

public class Lock1 {
//1. 先打印sms还是call？ 答案：先sms,因为synchronized锁是锁对象的，谁先拿到锁谁就先执行
    public static void main(String[] args) {
        //线程间交替执行demo
        Phone phone = new Phone();

        new Thread(()-> {
                phone.sendSMS();
        }).start();
        new Thread(()-> {
                phone.call();

        }).start();

    }

}
class  Phone{

    public synchronized void sendSMS(){
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        System.out.println("sms");
    }
    public synchronized void  call(){
        System.out.println("call");
    }
}

问题2：1. 先打印hello还是sms？ 答案：先hello

public class Lock2 {
//1. 先打印hello还是sms？ 答案：先hello
    public static void main(String[] args) {
        //线程间交替执行demo
        Phone2 phone = new Phone2();

        new Thread(()-> {
                phone.sendSMS();
        }).start();

        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }

        phone.hello();

    }

}
class  Phone2{

    public synchronized void sendSMS(){
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        System.out.println("sms");
    }
    public synchronized void  call(){
        System.out.println("call");
    }
    public  void  hello(){
        System.out.println("hello");
    }
}

问题3：先打印call还是sms？ 答：先call后sms，因为锁的是对象，两个对象分别调用就会各自执行，不被锁住

public class Lock3 {
//1. 先打印call还是sms？  答：先call后sms，因为锁的是对象，两个对象分别调用就会各自执行，不被锁住
    public static void main(String[] args) {
        //线程间交替执行demo
        Phone2 phone = new Phone2();
        Phone2 phone2 = new Phone2();

        new Thread(()-> {
                phone.sendSMS();
        }).start();

        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }

        new Thread(()-> {
            phone2.call();
        }).start();


    }

}
class  Phone3{

    public synchronized void sendSMS(){
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        System.out.println("sms");
    }
    public synchronized void  call(){
        System.out.println("call");
    }
    public  void  hello(){
        System.out.println("hello");
    }
}

问题4： 先打印call还是sms？
答：先sms，因为静态方法锁的是class对象

    public class Lock4 {
//1. 先打印call还是sms？  答：先sms，因为静态方法锁的是class对象
    public static void main(String[] args) {
        //线程间交替执行demo
        Phone4 phone = new Phone4();
        Phone4 phone2 = new Phone4();

        new Thread(()-> {
                phone.sendSMS();
        }).start();


        new Thread(()-> {
            phone2.call();
        }).start();


    }

}
class  Phone4{

    public static synchronized void sendSMS(){
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        System.out.println("sms");
    }
    public static synchronized void  call(){
        System.out.println("call");
    }
    public  void  hello(){
        System.out.println("hello");
    }
}

问题5：一个静态方法，一个普通方法，先执行call还是sms？ 答案：先call，因为静态方法锁的是class对象，call锁的是当前对象，也就是说他俩上的不是同一把锁

public class Lock5 {
//一个静态方法，一个普通方法，先执行call还是sms？，
// 答案：先call，因为静态方法锁的是class对象，call锁的是当前对象，也就是说他俩上的不是同一把锁
    public static void main(String[] args) {
        //线程间交替执行demo
        Phone5 phone = new Phone5();

        new Thread(()-> {
                phone.sendSMS();
        }).start();


        new Thread(()-> {
            phone.call();
        }).start();


    }

}
class  Phone5{

    public  synchronized void sendSMS(){
        try {
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        System.out.println("sms");
    }
    public static synchronized void  call(){
        System.out.println("call");
    }

}