Question

下面的代码显示了一个使用double点的矩形类，它们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能力，但我能想到的唯一方法是添加一个布尔参数，指定调用者是否想要制作副本或参考。

这是为了扩展性，虽然它可能不是最重要的，但我想要这个选项。但是，我不喜欢使用boolean参数实现它的方式。有没有办法让两个构造函数采用相同的参数，一个用于引用，一个用于复制？或原型中是否有等效的C ++参数自动定义，因此不需要调用者指定？我曾经考虑过使用varargs，但是调用者可以发送无限量的参数作为垃圾，可能导致堆栈溢出，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;
        }
    }


}

更新：感谢所有帮助我找出要做的事情。这就是我重新编码的方式。

/**
 * 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

有没有办法可以让两个构造函数采用相同的参数，一个用于引用，一个用于复制？

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

有没有办法让两个构造函数采用相同的参数......

没有。在Java中，每个构造函数必须具有不同的签名。

...或原型中是否有等效的C ++参数自动定义，因此不需要调用者指定？

没有直接的等价物。但是你可以这样：

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

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

在你的用例中它运行得非常好，在你有大量可选参数的用例中，这种方法变得笨拙和/或不可行。

但是，我同意工厂方法或工厂对象可以是更好的解决方案。

Answer 3

为什么不使用多态策略你可以这样做：

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。

可以复制或引用的构造函数

3 个答案: