Java 如何处理多个构造函数？

您好，我有分配问题，我需要在一个类中创建3个构造函数。为矩形中的两个角点初始化两个坐标。错误Eclipse给出了构造的“复制方法”和“此行上的多个标记”错误

public class Rectangle {

private double lowleftx;
private double lowlefty;

private double uprightx;
private double uprighty;


public Rectangle() {
    this.lowleftx = 0;
    this.lowlefty = 0;

    this.uprightx = 1;
    this.uprighty = 1;
}

public Rectangle(uprightx, uprighty) {

    this.lowleftx = 0;
    this.lowlefty = 0;
}
public Rectangle(uprightx, uprighty, lowleftx, lowlefty) {

    this.lowleftx = lowleftx;
    this.lowlefty = lowlefty;
    this.uprightx = uprightx;
    this.uprighty = uprighty;
}


public double getLowleftx() {
    return lowleftx;
}

public void setLowleftx(double lowleftx) {
    this.lowleftx = lowleftx;
}

public double getLowlefty() {
    return lowlefty;
}

public void setLowlefty(double lowlefty) {
    this.lowlefty = lowlefty;
}

public double getUprightx() {
    return uprightx;
}

public void setUprightx(double uprightx) {
    this.uprightx = uprightx;
}

public double getUprighty() {
    return uprighty;
}

public void setUprighty(double uprighty) {
    this.uprighty = uprighty;
}

---

}

您没有在构造函数参数中指定

double

数据类型，因此请按如下所示添加它：

   public Rectangle() {
        this.lowleftx = 0;
        this.lowlefty = 0;
        this.uprightx = 1;
        this.uprighty = 1;
    }

    public Rectangle(double uprightx, double uprighty) {
        this.lowleftx = 0;
        this.lowlefty = 0;
    }

    public Rectangle(double uprightx, double uprighty, 
            double lowleftx, double lowlefty) {
        this.lowleftx = lowleftx;
        this.lowlefty = lowlefty;
        this.uprightx = uprightx;
        this.uprighty = uprighty;
    }

---

如评论中所述，您忘记添加参数的类型：

public Rectangle(double uprightx, double uprighty...)

您可以通过使用其他构造函数的所有参数调用构造函数来优化代码：

public class Rectangle {

    private double lowLeftX;
    private double lowLeftY;
    private double upRightX;
    private double upRightY;

    public Rectangle(double lowLeftX, double lowLeftY, double upRightX, double upRightY) {
        this.lowLeftX = lowLeftX;
        this.lowLeftY = lowLeftY;
        this.upRightX = upRightX;
        this.upRightY = upRightY;
    }

    public Rectangle(double upRightX, double upRightY) {
        this(0, 0, upRightX, upRightY); // = Rectangle(0, 0, upRightX, upRightY)
    }

    public Rectangle() {
        this(0, 0, 1, 1); // = Rectangle(0, 0, 1, 1), or Rectangle(1, 1)
    }

    // ...
}

还可以创建一个类来表示“点”（具有X值和Y值的坐标），并在矩形类中使用它：

// Point.java
public class Point {

    private final double x;
    private final double y;

    public Point(double x, double y) {
        this.x = x;
        this.y = y;
    }

    // ...
}

// Rectangle.java
public class Rectangle {

    private final Point lowLeft;
    private final Point upRight;

    public Rectangle(final Point lowLeft, final Point upRight) {
        this.lowLeft = lowLeft;
        this.upRight = upRight;
    }

    public Rectangle(final Point upRight) {
        this(new Point(0, 0), upRight);
    }

    public Rectangle() {
        this(new Point(1, 1));
    }
}

---

因此，正如在其他答案中所看到的：您忘记了为参数指定类型

为了完整性：这就是你应该如何写下这个构造器：

public Rectangle() {
  this(1, 1);
}

public Rectangle(double x1, double y1) {
   this(0, 0, x1, y1);
}

public Rectangle(double x1, double y1, double x2, double y2) {
    this.x1 = x1;
    this.y1 = y1;
    this.x2 = x2;
    this.y2 = y2;
}

---

换句话说：避免重复代码。您可以将真正的“任务”工作委托给上一个ctor。然后，您希望使用易于阅读但仍有意义的名称。例如，在考虑坐标时，x1/y1比您的方法更容易掌握。

您忘记将参数类型输入构造函数<代码>公共矩形（直立X，直立）。它们应该类似于

公共矩形（double-uprightx，double-uprighty）

。公共矩形（双lowerleft，双upperright）{…提示：写下随机代码是学习编程语言的一种低效策略。首先学习书籍/教程，了解正确的语法。而不是写下“某物”然后假设这个社区的存在是为了帮助修复语法错误。一个巨大的错误：Eclipse根本不给你任何东西，它是虚拟机。Eclipse只是另一个IDE。不是downvoter，但我想这种方法是否“更好”取决于谁看它。我也听过很多“不要这样做”-主张辩护。您可能还希望将实际的双精度值传递给下一个构造函数，而不是int。编译器或JVM不会在意，是的，但它更可读，避免了问题，然后有人添加了一个

矩形（int，int）

构造函数（无论出于何种原因）。