+ (void) load and + (void) initialize

The + (void) Load method is called when the class is loaded into memory.

Run the program, load the system's class into memory first, and then load the custom class into memory. The + (void) Load method of the loaded class will be executed at this time.

The class is then loaded before it is called

(BOOL) Application: (UIApplication *) application didfinishlaunchingwithoptions: (nsdictionary *) launchOptions

Method.

+ (void) initialize. Called when a class is instantiated for the first time, so this method, like the + (void) Load method, is executed only once.

+ (void) load and + (void) initialize