Class loading
1. Concept: When the JVM uses a class for the first time, it finds the corresponding class file through the classPath, and obtains the relevant information of the class (package name, class name, parent class, properties, methods, etc.) from the class file, and the class stored in the JVM is loaded only once.
2 . Timing of class loading
(1) When an object of a class is created for the first time, the class is loaded first. Re-creating an object.
(2) Using static members (static attributes and static methods) in a class for the first time will lead to class loading.
(3) Subclass class loading will lead to class loading of its parent class: Creating a subclass object for the first time will use the static attributes and static methods of a subclass for the first time.