什么是“矩形”类？

Question

我正在尝试为学校完成一个项目。当我得到它时，它已部分完成。我无法测试我写的任何东西（除了布局，通过注释掉错误）。我有一个“无法将矩形解析为类型”的错误。以为我做错了什么，我在网上找到了这个完整的代码，我想我会看看有什么不同。我在这里遇到同样的错误……很多。是什么赋予了？注意*我不是想把这个程序传递进去，只是想看看它是如何工作的，因为我希望我的也做同样的事情。

    /** 
     * DrawRects.java
     * 
     * Allows the user to enter a number of rectangles using mouse input.
     * Keeps previous rectangles around.
     * Inspired by a C++ class demo by THC
     * 
     * @author Scot Drysdale on 4/19/00.  Modified to a JApplet 1/16/2012
     * Modified to add a "clear" button and use an ArrayList on 1/18/2012
     */


    import javax.swing.*;
    import java.awt.*;
    import java.awt.event.*;
    import java.util.ArrayList;

    public class DrawRects extends JApplet implements MouseListener,
            MouseMotionListener {
        private static final long serialVersionUID = 1L;
        private Point pressedPoint = null; // place where mouse pressed down
        private Rect currentRect = null; // rectangle being dragged.
        private ArrayList<Rect> boxes = new ArrayList<Rect>(); // a list of rectangles

        private static final Color[] colors = { Color.red, Color.cyan, Color.magenta,
                Color.yellow };
        private int colorIndex = 0; // index into colors of current color
        private JButton clearButton; // Button to clear the screen

        private static final int APPLET_WIDTH = 520; // Width of the applet
        private static final int APPLET_HEIGHT = 550; // Height of the applet
        private static final int CANVAS_WIDTH = 500; // Width of the canvas
        private static final int CANVAS_HEIGHT = 500; // Height of the applet

        /**
         * Initializes the applet
         */
        public void init() {
            addMouseListener(this);
            addMouseMotionListener(this);
            setSize(APPLET_WIDTH, APPLET_HEIGHT);

            Container cp = getContentPane(); // Content pane holds components
            cp.setLayout(new FlowLayout()); // Fill left to right, top to bottom

            Canvas canvas = new Canvas();
            cp.add(canvas); // The canvas is the only component

            // Make a button to clear the canvas, set the button's background
            // to cyan, and add it to the content pane.
            clearButton = new JButton("Clear");
            clearButton.setBackground(Color.cyan);
            clearButton.addActionListener(canvas);
            cp.add(clearButton);

            setVisible(true); // Makes the applet (and its components) visible
        }

        // Captures the position at which the mouse is initially pressed.
        // It creates a new currentRect object, because the previous one
        // will have been added to the ListOfRects.
        public void mousePressed(MouseEvent event) {
            pressedPoint = event.getPoint();
            currentRect = new Rect(pressedPoint.x, pressedPoint.y, 0, 0, Color.black);
        }

        /**
         * Gets the current position of the mouse as it is dragged and draws a
         * rectangle with this point and pressedPoint as corners. This creates a
         * rubberbanding rectangle effect.
         * 
         * @param event the event that caused this callback
         */
        public void mouseDragged(MouseEvent event) {
            if (currentRect != null) { // make sure that currentRect exists
                Point pt = event.getPoint();
                currentRect.setX(Math.min(pt.x, pressedPoint.x));
                currentRect.setY(Math.min(pt.y, pressedPoint.y));
                currentRect.setWidth(Math.abs(pt.x - pressedPoint.x));
                currentRect.setHeight(Math.abs(pt.y - pressedPoint.y));
                repaint();
            }
        }

        /**
         * Done dragging mouse, so add current Rect to ListOfRects.
         * 
         * @param event the event that caused this callback
         */
        public void mouseReleased(MouseEvent event) {
            if (currentRect != null) { // make sure that currentRect exists
                currentRect.setColor(colors[colorIndex]);
                colorIndex = (colorIndex + 1) % colors.length;
                boxes.add(currentRect);
                currentRect = null; // currentRect now in the list, so can't reuse it
            }
            repaint();
        }

        // Provide empty definitions for unused event methods.
        public void mouseClicked(MouseEvent event) {}
        public void mouseEntered(MouseEvent event) {}
        public void mouseExited(MouseEvent event) {}
        public void mouseMoved(MouseEvent event) {}

        /**
         * The canvas to draw upon
         */
        private class Canvas extends JPanel implements ActionListener {
            private static final long serialVersionUID = 1L;

            /**
             * Constructor to choose preferred size
             */
            public Canvas() {
                // Canvas is a subclass of JPanel. The way we set the size of
                // a JPanel is by the setPreferredSize method. It takes a reference to
                // a Dimension object, which just packages together a width and height.
                setPreferredSize(new Dimension(CANVAS_WIDTH, CANVAS_HEIGHT));
            }

            /**
             * Draw the rectangles
             * 
             * @param page the graphics object to draw on
             */
            public void paintComponent(Graphics page) {
                super.paintComponent(page);

                page.setColor(Color.black);
                page.drawRect(0, 0, CANVAS_WIDTH - 1, CANVAS_HEIGHT - 1); // Draw border

                for (Rect rectangle : boxes)        // Draw the saved rectangles
                    rectangle.fill(page);

                if (currentRect != null) // Draw the rectangle being dragged out (if exists)
                    currentRect.draw(page);
            }

            /**
             * Handle the button - provide an actionListener
             * @param event the event that caused this callback
             */
            public void actionPerformed(ActionEvent event) {
                boxes.clear();
                repaint();
            }
        }
    }

Answer 1

SDK 中没有名为 Rect 的内容。

当然，java.awt.Rectangle 可以帮助您完成任务。

但是，Rect 似乎只是您抓取的项目中的其他一些类，您忘记获取源代码（或者作者没有提供）。

它不需要特殊的import 或任何东西，如果它与DrawRects 位于同一个包中（从外观上看是默认包），或者如果它是@987654327 的内部类@（不是）。