java - 为什么我在 Java 的 main() 中再次声明静态字段可以成功？

Question

我声明了一个private static double fd，然后我在 main() 中再次声明了double fd。为什么我可以编译运行成功？

    public class HelloWorld {
    private static double fd = 1.0;

    public static void main(String[] args){
        System.out.println(fd); //1.0
        double fd = 2.0;
        System.out.println(fd); //2.0


    }
}

Answer 1

来自 JLS Scope of a Declaration部分:

The scope of a declaration is the region of the program within which the entity declared by the declaration can be referred to using a simple name, provided it is not shadowed.

来自 JLS Shadowing部分:

Some declarations may be shadowed in part of their scope by another declaration of the same name, in which case a simple name cannot be used to refer to the declared entity.

这意味着您不能使用简单名称 (df) 来引用类级别 df 变量，因为它被本地 df 变量遮蔽。但仍然有两个变量，您可以使用带有类名的静态变量:

public static void main(String[] args){
    System.out.println(fd); //1.0

    double fd = 2.0;

    System.out.println(fd); //2.0
    System.out.println(HelloWorld.fd);
}