Question

我正在尝试为BlueJ中的矩形类编写代码。当我编译我的代码时，我得到错误“类Rectangle中的构造函数Rectangle不能应用于给定的类型; required：无参数; found：int，int，int，int; reason：actual和formal参数列表的长度不同”。另外，我很困惑在哪里把公式放在一个矩形 - 宽x高。我正在尝试创建一个名为rectangle的类，我可以在另一个名为picture的类中使用它。我正试图用这堂课在房子里画一个烟囱。

这是我的代码：

import java.awt.*;

public class Rectangle
{
    private int height;
    private int width;
    private int xPosition;
    private int yPosition;
    private String color;
    private boolean isVisible;

/**
 * Create a new rectangle at default position with default color.
 */
    public Rectangle()
    {
        height = 20;
        width = 10;
        xPosition = 310;
        yPosition = 120;
        color = "red";
        isVisible = false;
    }

/**
 * Make this rectangle visible. If it was already visible, do nothing.
 */
    public void makeVisible()
    {
        isVisible = true;
        draw();
    }

/**
 * Make this rectangle invisible. If it was already invisible, do nothing.
 */
    public void makeInvisible()
    {
        erase();
        isVisible = false;
    }

/**
 * Move the rectangle a few pixels to the right.
 */
    public void moveRight()
    {
        moveHorizontal(20);
    }

/**
 * Move the rectangle a few pixels to the left.
 */
    public void moveLeft()
    {
        moveHorizontal(-20);
    }

/**
 * Move the rectangle a few pixels up.
 */
    public void moveUp()
    {
        moveVertical(-20);
    }

/**
 * Move the rectangle a few pixels down.
 */
    public void moveDown()
    {
        moveVertical(20);
    }

/**
 * Move the rectangle horizontally by 'distance' pixels.
 */
    public void moveHorizontal(int distance)
    {
        erase();
        xPosition += distance;
        draw();
    }

/**
 * Move the rectangle vertically by 'distance' pixels.
 */
    public void moveVertical(int distance)
    {
        erase();
        yPosition += distance;
        draw();
    }

/**
 * Slowly move the rectangle horizontally by 'distance' pixels.
 */
    public void slowMoveHorizontal(int distance)
    {
        int delta;

        if(distance < 0) 
    {
            delta = -1;
            distance = -distance;
    }
        else 
    {
            delta = 1;
    }

        for(int i = 0; i < distance; i++)
    {
            xPosition += delta;
            draw();
    }
}

/**
 * Slowly move the rectangle vertically by 'distance' pixels.
 */
    public void slowMoveVertical(int distance)
{
        int delta;

        if(distance < 0) 
    {
            delta = -1;
            distance = -distance;
    }
        else 
    {
            delta = 1;
    }

        for(int i = 0; i < distance; i++)
    {
            yPosition += delta;
            draw();
    }
}

/**
 * Change the size to the new size (in pixels). Size must be >= 0.
 */
    public void changeSize(int newWidth, int newHeight)
{
        erase();
        height = newHeight;
        width = newWidth;
        draw();
}

/**
 * Change the color. Valid colors are "red", "yellow", "blue", "green",
 * "magenta" and "black".
 */
    public void changeColor(String newColor)
{
        color = newColor;
        draw();
}

/**
 * Draw the rectangle with current specifications on screen.
 */
    private void draw()
{
        if(isVisible) {
            Canvas canvas = Canvas.getCanvas();
            canvas.draw(this, color,
                    **new Rectangle(xPosition, yPosition, width, height));**
            canvas.wait(10);
    }
}

/**
 * Erase the rectangle on screen.
 */
    private void erase()
{
        if(isVisible) {
            Canvas canvas = Canvas.getCanvas();
            canvas.erase(this);
    }
}

}

Answer 1

我对你的背景有很大的影响，但你的 draw()方法使用构造函数创建到目前为止还没有的Recangle新实例：

private void draw()
{
    if(isVisible) 
    {
        Canvas canvas = Canvas.getCanvas();
        canvas.draw(this, color,
                new Rectangle(xPosition, yPosition, width, height)); <-- Problem
        canvas.wait(10);
    }
}

您可以向您的类添加所需的构造函数，如下所示：

public Rectangle(xPos, yPos, width, height)
{
    this.height = height;
    this.width = width;
    this.xPosition = xPos;
    this.yPosition = yPos;
    color = "red";
    isVisible = false;
}

这会使有关draw()方法的错误消失，但我不确定这是解决问题所需的全部内容。你能给出更多背景吗？

我认为你的绘制方法应该是这样的：

private void draw()
{
    if(isVisible) 
    {
        Canvas canvas = Canvas.getCanvas();
        canvas.drawRect(color, this.xPosition, this.yPosition, this.width, this.height); 
        canvas.wait(10);
    }
}

Answer 2

你在主要方法中可能做的是：

Rectangle r = new Rectangle(10,10,10,10);

但是在你的类中只定义了无参数构造函数，因此错误。

您必须添加另一个构造函数：

    public Rectangle(int height, int width, int xPosition, int yPosition) {
        this.height = height ;
        this.width = width ;
        this.xPosition = xPosition ;
        this.yPosition = yPosition = 120;;
        color = "red";
        isVisible = false;
    }

个人观点：如果我没有记错的话，这是 Brucke Eckel 的书 Thinking in Java 中的一个例子。我知道他说要使用BlueJ，但在我看来IDE不是很好，为了你自己的好处，请查看NetBeans，Eclipse或IntelliJ。

BlueJ的矩形类

2 个答案: