用Java中的构造函数继承 [英] Inheritance with constructor in Java

问题描述

请告诉我以下代码中的问题？

Can you please tell me the problem in following code?

class boxdemo1 {
    public static void main(String args[]) {
        boxweight weightbox = new boxweight(2, 3, 5, 4);
        System.out.println(weightbox.volume());
    }
}

class boxinfo {
    int l, b, h;

    /*
     * boxinfo() { l=b=h=-1; }
     */
    boxinfo(int a, int b, int c) {
        l = a;
        this.b = b;
        h = c;
    }

    int volume() {
        return l * b * h;
    }
}

class boxweight extends boxinfo {
    int w;

    boxweight(int a, int b, int c, int w) {
        l = a;
        this.b = b;
        h = c;
        this.w = w;
    }
}

当我编译它时，它显示以下错误：
类boxinfo中的构造函数boxinfo不能应用于给定类型;需要
：int，int，int; found：无参数;实际和形式参数列表的长度不同。

When I compile it,it shows following error: "constructor boxinfo in class boxinfo cannot be applied to given types; required:int,int,int; found:no arguments; actual and formal argument lists differ in length."

但是当我编译它包括被注释的代码（即boxinfo（）构造函数）时，它会被编译。为什么需要包含默认构造函数？

But when I compile it including the code which is commented(i.e. boxinfo() constructor), it gets compiled. Why is it necessary to include default constructor?

推荐答案

通过设置 boxinfo（int a，int b ，int c）构造函数，java为 boxinfo 设置的默认无参数构造函数被删除。然后，当你调用 boxweight（int a，int b，int c，int w）构造函数时，因为 boxweight class继承自 boxinfo ，你隐式调用 boxinfo 中的默认构造函数，它刚被覆盖。

By setting your boxinfo(int a, int b, int c) constructor, the default no-parameters constructor set by java for boxinfo gets deleted. Then, when you call the boxweight(int a,int b,int c,int w) constructor, since the boxweight class inherits from boxinfo, you're implicitly calling the default constructor from boxinfo which just got overrided.

为了避免这种情况，要么在 boxinfo 中创建一个无参构造函数，要么显式调用 super（ a，b，c） in boxweight

To avoid this, either create yourself a no-argument constructor in boxinfo or call explicitly super(a, b, c) in boxweight

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