drawapplet.java

来自「Java the UML Way 书中所有源码」· Java 代码 · 共 159 行

/*
 * DrawApplet.java  E.L. 2001-08-18
 *
 */
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class DrawApplet extends JApplet {

  /* These ellipse attributes will be used the first time the ellipse is drawn */
  private static final String x = "70";
  private static final String y = "50";
  private static final String width = "50";
  private static final String height = "100";

  /*
   * The following variables will be used in the init() method,
   * in the listener class, and in the UserInputPanel class.
   */
  private Container guiContainer;
  private Drawing theDrawing;
  private JTextField xField = new JTextField(x);
  private JTextField yField = new JTextField(y);
  private JTextField widthField = new JTextField(width);
  private JTextField heightField = new JTextField(height);

  public void init() {
    guiContainer = getContentPane();

    UserInputPanel north = new UserInputPanel();
    guiContainer.add(north, BorderLayout.NORTH);

    theDrawing = new Drawing(x, y, width, height);
    guiContainer.add(theDrawing, BorderLayout.CENTER);

    ButtonPanel south = new ButtonPanel();
    guiContainer.add(south, BorderLayout.SOUTH);
  }

  /* Listens for button pushes */
  private class ButtonListener implements ActionListener {
    public void actionPerformed(ActionEvent event) {

      /* Gets new ellipse attributes and sends them to the drawing object */
      theDrawing.setX(xField.getText());
      theDrawing.setY(yField.getText());
      theDrawing.setWidth(widthField.getText());
      theDrawing.setHeight(heightField.getText());

      /* Gets the color of the button */
      String colorName = event.getActionCommand();
      Color color;
      if (colorName.equals("Red")) color = Color.red;
      else if (colorName.equals("Blue")) color = Color.blue;
      else color = Color.cyan;

      /* Sets the foreground color for the drawing */
      theDrawing.setForeground(color);

      /* Repaints the whole window */
      guiContainer.repaint();
    }
  }

  /* This class describes the northern panel. */
  private class UserInputPanel extends JPanel {
    public UserInputPanel() {
      /* The Gridlayout constructor takes the following arguments, in order:
         No. of rows, no. of columns, horizontal and vertical gap between the cells. */
      setLayout(new GridLayout(4, 2, 5, 5));
      JLabel label = new JLabel("X-value:", JLabel.RIGHT);
      add(label);
      add(xField);

      label = new JLabel("Y-value:", JLabel.RIGHT);
      add(label);
      add(yField);

      label = new JLabel("Width:", JLabel.RIGHT);
      add(label);
      add(widthField);

      label = new JLabel("Height:", JLabel.RIGHT);
      add(label);
      add(heightField);
    }
  }

  /* This class describes the southern panel. */
  private class ButtonPanel extends JPanel {
    public ButtonPanel() {
      ButtonListener theButtonListener = new ButtonListener();

      JButton redButton = new JButton("Red");
      redButton.setBackground(Color.red);
      redButton.addActionListener(theButtonListener);
      add(redButton);

      JButton blueButton = new JButton("Blue");
      blueButton.setBackground(Color.blue);
      blueButton.addActionListener(theButtonListener);
      add(blueButton);

      JButton cyanButton = new JButton("Cyan");
      cyanButton.setBackground(Color.cyan);
      cyanButton.addActionListener(theButtonListener);
      add(cyanButton);
    }
  }
}

/*
 * This class describes the drawing of an ellipse where the ellipse attributes
 * may be changed by the user. The class receives the attributes as texts.
 * If it is not possible to convert the text into a number, the corresponding
 * attribute gets the value 0. A litte message is sent to the console.
 */
class Drawing extends JPanel {
  private int x;
  private int y;
  private int width;
  private int height;
  public Drawing(String initX, String initY, String initWidth, String initHeight) {
    x = convertText(initX);
    y = convertText(initY);
    width = convertText(initWidth);
    height = convertText(initHeight);
  }

  public void setX(String newX) {
    x = convertText(newX);
  }

  public void setY(String newY) {
    y = convertText(newY);
  }

  public void setWidth(String newWidth) {
    width = convertText(newWidth);
  }

  public void setHeight(String newHeight) {
    height = convertText(newHeight);
  }

  public void paintComponent(Graphics window) {
    window.fillOval(x, y, width, height);
  }

  private int convertText(String text) {
    try {
      return Integer.parseInt(text);
    } catch (NumberFormatException e) {
      System.out.println("It's not possible to convert " + text + " into integer.");
      return 0;
    }
  }
}