synchronized用static修饰和不用static修饰的区别，synchronized同步代码块this和类的Class对象作为锁的区别。

看下面的例子：

package com.andy.juc;

public class SynchronizedTest {
    public static void main(String[] args) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                sub();
            }
        }).start();
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        SynchronizedTest.add();
    }


    public static synchronized void add(){
        System.out.println("hello add");
    }

    public static synchronized void sub()  {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("hello sub");
    }
}

一个是实例方法，一个是静态方法

package com.andy.juc;

public class SynchronizedTest {
    public static void main(String[] args) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                sub();
            }
        }).start();
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        new SynchronizedTest().add();
        
    }


    public  synchronized void add(){
        System.out.println("hello add");
    }

    public static synchronized void sub()  {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("hello sub");
    }
}

创建两个对象，分别调用自己的实例方法，不会有并发问题。

package com.andy.juc;

public class SynchronizedTest {
    public static void main(String[] args) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                new SynchronizedTest().sub();
            }
        }).start();
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        new SynchronizedTest().add();

    }


    public  synchronized void add(){
        System.out.println("hello add");
    }

    public  synchronized void sub()  {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("hello sub");
    }
}

同一个对象，锁资源相互排斥

package com.andy.juc;

public class SynchronizedTest {
    public static void main(String[] args) {
        SynchronizedTest synchronizedTest = new SynchronizedTest();
        new Thread(new Runnable() {
            @Override
            public void run() {
                synchronizedTest.sub();
            }
        }).start();
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        synchronizedTest.add();

    }


    public  synchronized void add(){
        System.out.println("hello add");
    }

    public  synchronized void sub()  {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("hello sub");
    }
}

同步代码块，用类的Class对象来加锁，互斥

package com.andy.juc;

public class SynchronizedTest {
    public static void main(String[] args) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                new SynchronizedTest().sub();
            }
        }).start();
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        new SynchronizedTest().add();

    }


    public   void add(){
        synchronized(SynchronizedTest.class){
            System.out.println("hello add");
        }
    }

    public  void sub()  {
        synchronized(SynchronizedTest.class){
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("hello sub");
        }

    }
}