Final class variable local variable initialization

Local variables do not have a default value: So be sure to initialize them before using them, or initialize them when they are declared, or declare them after the assignment (whether final or not):
int a=9;
int b;
b=0;

class's member Variable:
Non-final variables have default initial values, so you can assign values that are not displayed
But final to initialize: The first initialization is the time of declaration: final int a=0;
The second is to declare in the current class and then assign a value in the constructor, and if there are multiple constructors, each is assigned a value.