为什么不能从构造函数是私有的类继承？ [英] Why can you not inherit from a class whose constructor is private?

问题描述

为什么Java不允许从构造函数是私有的类继承？

Why does Java disallow inheritance from a class whose constructor is private?

推荐答案

Java不会阻止使用私有构造函数对类进行子类化。

Java doesn't prevent sub-classing of class with private constructors.

public class Main {
    static class A {
        private A() {
            System.out.println("Subclassed A in "+getClass().getName());
        }
    }

    static class B extends A {
        public B() {

        }
    }

    public static void main(String... ignored) {
        new B();
    }
}

打印

Subclassed A in Main$B

什么它可以防止无法访问其超类的任何构造函数的子类。这意味着私有构造函数不能在另一个类文件中使用，并且包本地构造函数不能在另一个包中使用。

What it prevents is sub-classes which cannot access any constructors of its super class. This means a private constructor cannot be used in another class file, and a package local constructor cannot be used in another package.

在这种情况下，你唯一的选择是代表团。您需要调用工厂方法来创建超级类的实例并将其包装起来。

In this situation, the only option you have is delegation. You need to call a factory method to create an instance of the "super" class and wrap it.

这篇关于为什么不能从构造函数是私有的类继承？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！