来自超级类的受保护变量在不同包中的子类不可见 [英] protected variable from super class not visible from subclass in different package

问题描述

我有两个类在不同的包中如下
这是包库中的基类。

I have two classes in different packages as follows This is the base class in package library.

package library;

public class Book{

    public int varPublic;
    protected int varProtected;
    private int varPrivate;
    int varDefault;
}

这是构建包的子类。

package building;

import library.Book;

public class StoryBook extends Book {


    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Book book = new Book();
        book.varPublic = 10;
        book.varProtected = 11;


    }

}

我的理解是，变量var.Protected应该在StoryBook类中可见，但是我收到错误。我试图从eclipse和命令提示符执行这个代码。

my understanding is that the variable "var.Protected" should be visible in the class StoryBook but i am getting an error. I have tried to execute this code from eclipse and command-prompt.

任何人都可以查看这个

推荐答案

作为声明类的子类的其他包中的类只能访问自己继承的保护的成员。

Classes in other packages that are subclasses of the declaring class can only access their own inherited protected members.

public class StoryBook extends Book {
    public StoryBook() {
        System.out.println(this.variable); // this.variable is visible
    }
}

...但不是其他对象的继承保护成员。

... but not other objects' inherited protected members.

public class StoryBook extends Book {
    public StoryBook() {
        System.out.println(this.variable); // this.variable is visible
    }

    public boolean equals(StoryBook other) {
        return this.variable == other.variable; // error: StoryBook.variable is not visible
    }
}

另外在这篇文章中采取

为什么不能从子类访问超类的受保护成员通过使用超类'参考？

Why a protected member of a superclass can't be accessed from a subclass by using a superclass' reference?

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