可以复制或引用的java构造函数

Question

下面的代码显示了一个使用double点的矩形类，这些点也存储在一个对象中。矩形和矩形中的点是不可变的，因为它们不需要更改。我想提供复制（创建新的点对象）或引用构造函数中提供的点的功能，但我能想到的唯一方法是添加一个布尔参数，指定调用方是否希望创建副本或引用

这是为了扩展性，虽然它可能不是最重要的，但我希望这个选项。然而，我不喜欢用布尔参数实现它的方式。有没有办法让两个构造函数使用相同的参数，一个用来引用，一个用来复制？或者在原型中有一个等价于C++参数自动定义，所以它不需要由调用方指定吗？我曾考虑过使用varargs，但调用方可能会将无限的参数作为垃圾发送，可能会导致堆栈溢出，我认为

/**
 * An immutable, double-precision floating-point (64-bit doubles x4) rectangle.
 * The rectangle can be made to reference existing points, or to create new points. Since the points
 * are also immutable, this is acceptable, as it is guaranteed they cannot change.
 * @author Bill
 */
public class DoubleRect {
    public final DoublePoint topLeft;
    public final DoublePoint bottomRight;

    public DoubleRect(DoublePoint setTopLeft, DoublePoint setBottomRight, boolean makeCopies) {
        if(makeCopies == true) {        
            topLeft = new DoublePoint(setTopLeft);
            bottomRight = new DoublePoint(setBottomRight);
        }
        else {
            topLeft = setTopLeft;
            bottomRight = setBottomRight;
        }
    }


}

帮我弄明白了什么。我就是这样重新编码的

/**
 * An immutable, double-precision floating-point (64-bit) rectangle.
 * The rectangle can be made to reference existing points, or to create new points. Since the points
 * are also immutable, referencing the points is acceptable, as it is guaranteed they cannot change.
 * @author Bill
 */
public class DoubleRect {
    public final DoublePoint topLeft;
    public final DoublePoint bottomRight;

    /**
     * This constructor will reference the passed objects rather than duplicating them.
     * See the static factory method createWithClonedPoints() for making internal copies of the point objects
     * @param setTopLeft Double point designating the top left coordinate
     * @param setBottomRight Double point designating the bottom right coordinate
     */
    public DoubleRect(DoublePoint setTopLeft, DoublePoint setBottomRight) {
        topLeft = setTopLeft;
        bottomRight = setBottomRight;
    }

    /**
     * This constructor will create new immutable points within this object using the coordinates specified
     */
    public DoubleRect(double top, double left, double right, double bottom) {
        topLeft = new DoublePoint(left, top);
        bottomRight = new DoublePoint(right, bottom);
    }

    public static DoubleRect createWithClonedPoints(DoublePoint topLeft, DoublePoint bottomRight) {
        return new DoubleRect(topLeft.x, topLeft.y, bottomRight.x, bottomRight.y);
    }


}

Answer 1

Is there a way I can make two constructors taking the same parameters, one to make a reference and one to make copies?

在这种情况下，建议使用多个静态工厂方法，而不是构造函数

Answer 2

Is there a way I can make two constructors taking the same parameters ...

不可以。在Java中，每个构造函数必须有不同的签名

... or is there an equivalent to C++ parameter auto definition in the prototype so it doesn't need to be specified by the caller?

不，没有直接的等价物。然而，你可以这样做：

public DoubleRect(DoublePoint topLeft, DoublePoint bottomRight,
         boolean makeCopies) {
    ...
}

public DoubleRect(DoublePoint topLeft, DoublePoint bottomRight) {
    this(topLeft, bottomRight, false);
}

在您的用例中，它工作得非常好，在您有许多可选参数的用例中，这种方法变得很难操作和/或不可行

---

然而，我同意工厂方法或工厂对象可能是更好的解决方案

Answer 3

为什么不使用多态性策略呢？你可以这样做：

public class DoubleRect {
    public final DoublePoint topLeft;
    public final DoublePoint bottomRight;

    public DoubleRect() {
       topLeft = new DoublePoint();
       bottomRight = new DoublePoint();
    }

public DoubleRect(DoublePoint setTopLeft, DoublePoint setBottomRight)
{
   topLeft = setTopLeft;
   bottomRight = setBottomRight;
}


}

这种类型的构造函数声明在java上有效