在Java中构建一个复制构造函数 [英] Building a copy constructor in Java

问题描述

如何构建接收另一个点（x，y）并复制其值的复制构造函数？

How do I build a copy constructor that receive another point (x,y) and copy its values ?

我决定签名： public Point1（Point1 other），但我不知道该写什么...

I decide a signature: public Point1 (Point1 other) , but I don't know what to write in it...

Point类看起来像： / p>

The Point class looks like:

public class Point1

{
    private int _x ,  _y;    
    public Point1 (Point1 other)
    {
        ...
        ...
    }
//other more constructors here...

}

我试过： b
$ b

I tried:

public Point1 (Point1 other)
{
    _x = other._x ;
    _y = other._y;
}

但我几乎肯定我可以做得更好..

But I almost sure I can do it better..

thnx

推荐答案

不，你的尝试

public Point1(Point1 other)
{
    _x = other._x ;
    _y = other._y;
}

是绝对精细...（我已更正参数类型。

is absolutely fine... (I've corrected the parameter type.)

我会试着让 _x 和 _y final，并使类最终，但这是因为我喜欢不变的类型。其他人肯定有不同的意见：）

I'd be tempted to make _x and _y final, and make the class final, but that's because I like immutable types. Others definitely have different opinions :)

在继承层次结构上克隆有点棘手 - 层次结构中的每个类都必须有一个相关的构造函数，将任何参数传递给超类构造函数，然后只复制其自己的字段。例如：

Cloning on an inheritance hierarchy is slightly trickier - each class in the hierarchy has to have a relevant constructor, pass whatever argument it's given to the superclass constructor, and then copy just its own fields. For example:

public class Point2 extends Point1    
{
    private int _z;
    public Point2(Point2 other)
    {
        super(other);
        this._z = other._z;
    }
}

这在实现方面并不糟糕，您想要忠实克隆 Point2 ，您需要知道是 Point2 调用正确的构造函数。

That's not too bad on the implementation side, but if you want to faithfully clone a Point2 you need to know it's a Point2 in order to call the right constructor.

实现可克隆允许这样做更简单一点，考虑周围...基本上克隆对象不是那么简单，它可能会出现:)（我敢肯定有效的Java中有一个条目，如果你没有副本，现在买一个。）

Implementing Cloneable allows this to be done a bit more simply, but there are other things to consider around that... basically cloning objects isn't as simple as it might appear :) (I'm sure there's an entry in Effective Java for it. If you don't have a copy, buy one now.)

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