使用子类名访问父类静态字段不会加载子类？ [英] Accessing parent class static field using child class name doesn't load the child class?

问题描述

class A {
    static int super_var = 1;
    static {
        System.out.println("super");
    }
}

class B extends A {
    static int sub_var = 2;
    static {
        System.out.println("sub");
    }    
}
public class Demo{
    public static void main(String []args){
        System.out.println(B.super_var);
    }
}

输出为：

super
1

这意味着孩子班级不会加载或任何其他东西？它是如何工作的？

this means that the child class not going to load or any other thing? how is it works?

推荐答案

当您访问 static 字段时子类引用上的超类，只有声明该字段的类才会被加载和初始化，在这种情况下它是 A 。这在 JLS§ 12.4.1 - 初始化发生时：

When you access the static fields of a super class on subclass reference, only the class that declares the field will be loaded and initialized, in this case it is A. This is specified in JLS §12.4.1 - When Initialization Occurs:

对 static field（§8.3.1.1）导致只初始化
实际声明它的类或接口，即使可能通过子类名称引用
，子接口或实现接口的
类。

A reference to a static field (§8.3.1.1) causes initialization of only the class or interface that actually declares it, even though it might be referred to through the name of a subclass, a subinterface, or a class that implements an interface.

强调我的。

所以在你的代码中，类 B 甚至不会被初始化，因此它的 static 块不会被执行。

So in your code, class B would not even be initialized, and hence its static block would not be executed.

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