Java在子类构造函数中初始化基类字段 [英] java initialize base class fields in subclass constructor

问题描述

这是有关Java子类的一个非常基本的问题，我仍然不明白...

This is a very basic question about subclasses in java, I still don't get it...

假设我有一个具有三个字段且仅具有默认构造函数的超类:

Suppose I have a superclass with three fields and with only the default constructor:

public class Superclass {
    public int a;
    public int b;
    public int c;
}

，我想添加一个字段x.我不能更改 Superclass ，所以我创建了一个子类:

and I want to add a field x. I cannot change Superclass, so I make a subclass:

public class Subclass extends Superclass {
    public int x;
    public Subclass(Superclass s) {
        super();
        // what to do??
    }
}

我现在想从现有的 Superclass 对象生成一个 Subclass 对象:

I now want to generate a Subclass object from an existing Superclass object:

Superclass s = new Superclass();
s.a = "a";
s.b = "b";
Subclass sc = new Subclass(s);
sc.x = "x";

这样我仍然可以访问 sc.a ， sc.b 等.

such that I can still access sc.a, sc.b etc.

如何最好地做到这一点，而不必在子类的构造函数中手动分配所有这些字段?

How can I best do this without assigning all these fields 'by hand' in the constructor of the subclass?

推荐答案

您必须在基类构造函数或子类中为变量分配一个值.

You have to assign a value to the variables either in the base-class constructor or in the child class.

您可以在子类中声明参数化的构造函数，以将值分配给超类中的变量

You can declare a parameterized constructor in sub-class to assign the value to a variable in the superclass

class Subclass extends Superclass {
public int x;
public Subclass(int a,int b, int c,int x) {
    super();
    this.x = x;
    this.a=a;
    this.b=b;
    this.c=c;
 }
}

或者您可以在BaseClass和子类中声明参数化的构造函数，而不是调用 super()，而是调用经过参数化的构造函数 super(a，b，c)

Or you can declare a parameterized constructor in BaseClass, and in child class, instead of calling super(), call that parametrized constructorsuper(a,b,c)

class Superclass {
public int a;
public int b;
public int c;

public Superclass(int a, int b, int c) {
    this.a = a;
    this.b = b;
    this.c = c;
 }   
}

class Subclass extends Superclass {
public int x;

public Subclass(int a,int b, int c,int x) {
    super(a,b,c);
    this.x = x;
 }
}

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