/*  * SelectionDemo.java requires one other file: *   images/starfield.gif */import javax.swing.BoxLayout;import javax.swing.ImageIcon;import javax.swing.JFrame;import javax.swing.JLabel;import javax.swing.event.MouseInputAdapter;import java.awt.*;import java.awt.event.MouseEvent;/*  * This displays an image.  When the user drags within * the image, this program displays a rectangle and a string * indicating the bounds of the rectangle. */public class SelectionDemo {    JLabel label;    static String starFile = "images/starfield.gif";        private void buildUI(Container container, ImageIcon image) {        container.setLayout(new BoxLayout(container,                                          BoxLayout.PAGE_AXIS));                                                  SelectionArea area = new SelectionArea(image, this);        container.add(area);        label = new JLabel("Drag within the image.");        label.setLabelFor(area);        container.add(label);        //Align the left edges of the components.        area.setAlignmentX(Component.LEFT_ALIGNMENT);        label.setAlignmentX(Component.LEFT_ALIGNMENT); //redundant    }    public void updateLabel(Rectangle rect) {        int width = rect.width;        int height = rect.height;        //Make the coordinates look OK if a dimension is 0.        if (width == 0) {            width = 1;        }        if (height == 0) {            height = 1;        }        label.setText("Rectangle goes from ("                      + rect.x + ", " + rect.y + ") to ("                      + (rect.x + width - 1) + ", "                      + (rect.y + height - 1) + ").");    }    /** Returns an ImageIcon, or null if the path was invalid. */    protected static ImageIcon createImageIcon(String path) {        java.net.URL imgURL = SelectionDemo.class.getResource(path);        if (imgURL != null) {            return new ImageIcon(imgURL);        } else {            System.err.println("Couldn't find file: " + path);            return null;        }    }    /**     * Create the GUI and show it.  For thread safety,      * this method should be invoked from the      * event-dispatching thread.     */    private static void createAndShowGUI() {        //Create and set up the window.        JFrame frame = new JFrame("SelectionDemo");        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        //Set up the content pane.        SelectionDemo controller = new SelectionDemo();        controller.buildUI(frame.getContentPane(),                           createImageIcon(starFile));        //Display the window.        frame.pack();        frame.setVisible(true);    }    public static void main(String[] args) {        //Schedule a job for the event-dispatching thread:        //creating and showing this application's GUI.        javax.swing.SwingUtilities.invokeLater(new Runnable() {            public void run() {                createAndShowGUI();             }        });    }        private class SelectionArea extends JLabel {        Rectangle currentRect = null;        Rectangle rectToDraw = null;        Rectangle previousRectDrawn = new Rectangle();        SelectionDemo controller;            public SelectionArea(ImageIcon image, SelectionDemo controller) {            super(image); //This component displays an image.            this.controller = controller;            setOpaque(true);            setMinimumSize(new Dimension(10,10)); //don't hog space                MyListener myListener = new MyListener();            addMouseListener(myListener);            addMouseMotionListener(myListener);        }            private class MyListener extends MouseInputAdapter {            public void mousePressed(MouseEvent e) {                int x = e.getX();                int y = e.getY();                currentRect = new Rectangle(x, y, 0, 0);                updateDrawableRect(getWidth(), getHeight());                repaint();            }                public void mouseDragged(MouseEvent e) {                updateSize(e);            }                public void mouseReleased(MouseEvent e) {                updateSize(e);            }                /*              * Update the size of the current rectangle             * and call repaint.  Because currentRect             * always has the same origin, translate it             * if the width or height is negative.             *              * For efficiency (though             * that isn't an issue for this program),             * specify the painting region using arguments             * to the repaint() call.             *              */            void updateSize(MouseEvent e) {                int x = e.getX();                int y = e.getY();                currentRect.setSize(x - currentRect.x,                                    y - currentRect.y);                updateDrawableRect(getWidth(), getHeight());                Rectangle totalRepaint = rectToDraw.union(previousRectDrawn);                repaint(totalRepaint.x, totalRepaint.y,                        totalRepaint.width, totalRepaint.height);            }        }            protected void paintComponent(Graphics g) {            super.paintComponent(g); //paints the background and image                //If currentRect exists, paint a box on top.            if (currentRect != null) {                //Draw a rectangle on top of the image.                g.setXORMode(Color.white); //Color of line varies                                           //depending on image colors                g.drawRect(rectToDraw.x, rectToDraw.y,                            rectToDraw.width - 1, rectToDraw.height - 1);                    controller.updateLabel(rectToDraw);            }        }            private void updateDrawableRect(int compWidth, int compHeight) {            int x = currentRect.x;            int y = currentRect.y;            int width = currentRect.width;            int height = currentRect.height;                //Make the width and height positive, if necessary.            if (width < 0) {                width = 0 - width;                x = x - width + 1;                 if (x < 0) {                    width += x;                     x = 0;                }            }            if (height < 0) {                height = 0 - height;                y = y - height + 1;                 if (y < 0) {                    height += y;                     y = 0;                }            }                //The rectangle shouldn't extend past the drawing area.            if ((x + width) > compWidth) {                width = compWidth - x;            }            if ((y + height) > compHeight) {                height = compHeight - y;            }                      //Update rectToDraw after saving old value.            if (rectToDraw != null) {                previousRectDrawn.setBounds(                            rectToDraw.x, rectToDraw.y,                             rectToDraw.width, rectToDraw.height);                rectToDraw.setBounds(x, y, width, height);            } else {                rectToDraw = new Rectangle(x, y, width, height);            }        }    }}