如何通过静态方法检查静态和非静态变量的可访问性？

static 关键字是Java中的非访问修饰符，可用于变量、方法和代码块。 Java中的静态变量属于类，即它只在执行开始时初始化一次。通过使用静态变量，类的所有实例共享一个副本，并且可以通过类名直接访问它们，不需要任何实例。静态方法同样属于类而不属于实例，它只能访问静态变量而不能访问非静态变量。

例1：静态方法可以访问静态变量。

Java

// Java program to check accessibility
// of static variables inside
// static methods
 
class GFG {
 
    // declaring variable 'a' as static
    static int a = 5;
 
    // main is also a static type
    public static void main(String args[])
    {
 
        // accessing value of
        // static variable
        System.out.println("Static variable:" + a);
    }
}

输出

Static variable:5

示例 2：我们无法访问静态方法中的非静态变量。

Java

// Java program to check accessibility
// of non - static variables inside
// static methods
 
class GFG {
 
    // declaring variable 'a' as non - static
    int a = 5;
 
    // main is also a static type
    public static void main(String args[])
    {
 
        // accessing value of
        // non - static variable
        System.out.println("Non - Static variable:" + a);
    }
}

输出

prog.java:16: error: non-static variable a cannot be referenced from a static context
    System.out.println("Non - Static variable:" + a);
                                                  ^
1 error

示例 3：

Java

// Java Program to demonstrate the accessibility
// of static and non-static variables
// by static method
 
class Student {
 
    // initialized to zero
    int a;
 
    // initialized to zero when class is loaded
    // but not for each object created.
    static int b;
 
    // Constructor
    Student()
    {
 
        // incrementing static variable b
        b++;
    }
 
    // method for printing
    public void printData()
    {
        System.out.println("Value of a = " + a);
        System.out.println("Value of b = " + b);
    }
 
    /*public static void increment(){
     a++;
    }*/
}
 
// Driver class
class GFG {
 
    // main is a static block
    public static void main(String args[])
    {
 
        // creating instance
        Student s1 = new Student();
 
        s1.printData();
 
        // directly accessing variable 'b'
        // by class name because it is static
        Student.b++;
 
        s1.printData();
    }
}

输出

Value of a = 0
Value of b = 1
Value of a = 0
Value of b = 2

在上面的程序中，如果我们删除 increment 方法的注释，则会引发错误，因为 increment 方法是静态的，而变量 a 是非静态的，我们已经知道静态方法不能访问非静态变量。