What do Java class variables mean?

1. Description

Class variables are also called static variables. They are declared with the static keyword in the class, but must be outside the method.

No matter how many objects a class creates, a class has only one copy of the class variable.

Static variables are rarely used except when declared as constants. Static variables refer to variables declared as public/private, final and static types. Static variables cannot be changed after initialization.

Static variables are stored in the static storage area. Often declared as constants, variables are rarely declared using static alone.

Static variables are created when accessed for the first time and destroyed when the program ends.

Have similar visibility to instance variables. However, many static variable declarations are of public type in order to be seen by users of the class.

2. Example

public class Employee {
    //salary是静态的私有变量
    private static double salary;
    // DEPARTMENT是一个常量
    public static final String DEPARTMENT = "开发人员";
 
    public static void main(String[] args) {
        //我们可以先定义，然后再初始化之后使用
        salary = 10000;
        //输出结果：开发人员平均工资:10000.0
        System.out.println(DEPARTMENT + "平均工资:" + salary);
    }
}

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