BlueJ 的矩形类

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，我收到错误“矩形类中的构造函数矩形不能应用于给定类型；必需：无参数；找到：int、int、int、int；原因：实际和形式参数列表的长度不同”。另外，我对在哪里放置矩形的公式 - 宽度 x 高度感到困惑。我正在尝试创建一个名为矩形的类，我可以在另一个名为图片的类中使用它。我正在尝试使用此类在房屋图片上制作烟囱。

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

我对你的上下文是什么感到很模糊，但你的 draw() 方法使用构造函数来创建一个新的 Recangle 实例，你目前还没有：

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

您可以将所需的构造函数添加到您的类中，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;
}

这将使您的draw() 方法的错误消失，但我不确定这是否是您解决问题所需的全部。能否提供更多背景信息？

我认为你的 draw 方法应该看起来像这样：

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

你可能在你的 main 方法中做的是这样的：

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

但是在您的类中只定义了无参数构造函数，因此出现错误。

你将不得不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：如果我没记错的话，这是Brucke Eckel 的Thinking in Java 一书中的一个例子。我知道他说要使用BlueJ，但我认为IDE不是很好，为了您自己的利益，请查看NetBeans，Eclipse或IntelliJ。