Synchronized usage in Java

1. the synchronized keyword has two scopes:

1) In an object instance, synchronized aMethod () {} can prevent multiple threads from simultaneously accessing the synchronized Method of the object (if an object has multiple synchronized methods, as long as a thread accesses one of the synchronized methods, other threads cannot simultaneously access any of this object's synchronized methods ). At this time, the synchronized methods of different object instances are irrelevant. That is to say, other threads can access the synchronized Method in another object instance of the same class at the same time;

2) is the scope of a class. synchronized static aStaticMethod {} prevents multiple threads from simultaneously accessing the synchronized static method in this class. It can work on all object instances of the class.

2. In addition to using the synchronized keyword before the method, the synchronized keyword can also be used in a block in the method, indicating that only the resources in this block are mutually exclusive. Usage: synchronized (this) {/* block */}. Its scope is the current object;

3. the synchronized keyword cannot be inherited. That is to say, the method of the base class synchronized f () {} is not automatically synchronized f () {} in the inheritance class (){}, instead, it becomes f (){}. You need to explicitly specify a method of the inherited class as the synchronized method;