Java class Lock and Object lock (instance lock) synchronization problem

It is well known that synchronized can be used to modify methods and blocks of code for classes or objects.

When a code block is decorated, synchronized (object) acts on the object, constraining only that object.

Synchronized (class) acts on a class, constraining all objects of the class.

When modifying a method, the synchronized modifies the static method for the class. Used for objects when modifying non-static methods.

Note Class and object locks are two different locks, and they do not have a synchronization relationship.

Because of the static variable, it can be called by the static method, or it can be called by a non-static method, and when both are synchronized decorated, there is a potential synchronization problem.

Therefore, multi-threading static variables as far as possible only static method calls, otherwise there will be synchronization confusion.

Class Test implements runnable{    public  static  int num = 0;    Public synchronized void Changenum () {        num++;        SYSTEM.OUT.PRINTLN (num);    }      Public synchronized static void Addnum () {        num++;        SYSTEM.OUT.PRINTLN (num);    }    @Override public    Void Run () {for        (int i = 0; i < i++) {            changenum ();            Addnum ();            try {                thread.sleep (5);            } catch (Interruptedexception IE) {}}} public    static void Main (string[] args) {         test test = new Test ();        thread T1 = new thread (test);        Thread t2 = new Thread (test);        T1.start ();        T2.start ();    }}

If you synchronize, the result should be 8000, but not.

Java class Lock and Object lock (instance lock) synchronization problem