Three locking methods of the bottom layer of synchronized: (3.21-3.27)

Decorate common methods : It modifies the instance object of the class , Also called object lock , There are two scenarios :1. Two threads execute the same lock object in two synchronization methods , Will form mutually exclusive scenes ;( Because the objects of the lock are the same )
                                              2. Two objects execute the same synchronization method in two threads , Not mutually exclusive ;( The objects of the lock are two )

Modified static method : Decorated class objects , Also called class lock ; Three usage scenarios :1. A class object executes different synchronization methods in two different threads , They are mutually exclusive ; Because it is the same class object lock
                                        2. A class object executes a normal locking method and a static locking method , Will also be mutually exclusive , Like the above, it is a class object lock
                                        3. Static method locks and ordinary method locks executed by an object , No mutual exclusion , Because the mechanisms of the two objects are different ;

Decorated code block :1. Decorate common methods , Regular in parentheses (this) In itself ;2. Decorated class object ( This kind .class);3. Modify arbitrarily defined Object Objects of type are in parentheses ;