Short integer variable is a kind of integer variable. Variable, which comes from mathematics, is an abstract concept in computer language. It can store calculation results or represent numerical values. Variables can be accessed by their names. In imperative languages, variables are usually variable; But in a purely functional language (such as Haskell), variables may be immutable.

1. Instance variables can use access descriptors.

2. Instance variables have default values. The default value of number is 0, boolean is false, and object reference is NULL.

3. You can directly access the instance variable by calling the name in the class. However, fully qualified names should be used in static methods and different classes.

4. Instance variables are variables belonging to instances of a class, also known as member variables, and have not been statically modified. Instance variables can only be manipulated by instance of class name+dot operator+variable.

5. Class variable: Also known as static variable, it is declared with the static keyword in the class, but it is outside the method, constructor or block.

6. Each class has only one class variable, no matter how many objects there are in this class.

7. Class variables are rarely used except as constants. Constants are variables declared as public, private, final and static.

8. Static variables are stored in static memory, and they are rarely used instead of declaring end or using a constant public or private.