9.14-buttondemo.java

介绍有关java的资料 课件 相当一本书籍 里面都是很基础的知识

// ButtonDemo.java: Use buttons to move message in a panel
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.*;

public class ButtonDemo extends JFrame
  implements ActionListener
{
  // Declare a panel for displaying message
  private MessagePanel messagePanel;

  // Declare two buttons to move the message left and right
  private JButton jbtLeft, jbtRight;

  // Main method
  public static void main(String[] args)
  {
    ButtonDemo frame = new ButtonDemo();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setVisible(true);
  }

  public ButtonDemo()
  {
    setTitle("Button Demo");

    // Create a MessagePanel instance and set colors
    messagePanel = new MessagePanel("Welcome to Java");
    messagePanel.setBackground(Color.yellow);

    // Create Panel jpButtons to hold two Buttons "<=" and "right =>"
    JPanel jpButtons = new JPanel();
    jpButtons.setLayout(new FlowLayout());
    jpButtons.add(jbtLeft = new JButton());
    jpButtons.add(jbtRight = new JButton());

    // Set button text
    jbtLeft.setText("<=");
    jbtRight.setText("=>");

    // Set keyboard mnemonics
    jbtLeft.setMnemonic('L');
    jbtRight.setMnemonic('R');

    // Set icons
    //jbtLeft.setIcon(new ImageIcon("images/left.gif"));
    //jbtRight.setIcon(new ImageIcon("images/right.gif"));

    // Set toolTipText on the "<=" and "=>" buttons
    jbtLeft.setToolTipText("Move message to left");
    jbtRight.setToolTipText("Move message to right");

    // Place panels in the frame
    getContentPane().setLayout(new BorderLayout());
    getContentPane().add(messagePanel, BorderLayout.CENTER);
    getContentPane().add(jpButtons, BorderLayout.SOUTH);

    // Register listeners with the buttons
    jbtLeft.addActionListener(this);
    jbtRight.addActionListener(this);
  }

  // Handle button events
  public void actionPerformed(ActionEvent e)
  {
    if (e.getSource() == jbtLeft)
    {
      left();
    }
    else if (e.getSource() == jbtRight)
    {
      right();
    }
  }

  // Move the message in the panel left
  private void left()
  {
    int x = messagePanel.getXCoordinate();
    if (x > 10)
    {
      // Shift the message to the left
      messagePanel.setXCoordinate(x-10);
      messagePanel.repaint();
    }
  }

  // Move the message in the panel right
  private void right()
  {
    int x = messagePanel.getXCoordinate();
    if (x < getSize().width - 20)
    {
      // Shift the message to the right
      messagePanel.setXCoordinate(x+10);
      messagePanel.repaint();
    }
  }
}



// MessagePanel: Display a message on a JPanel

class MessagePanel extends JPanel
{
  private String message = "Welcome to Java"; // Message to display

  // (x, y) coordinates where the message is displayed
  private int xCoordinate = 20;
  private int yCoordinate = 20;

  // Indicating whether the message is displayed in the center
  private boolean centered;

  // Default constructor
  public MessagePanel()
  {
  }

  // Contructor with a message parameter
  public MessagePanel(String message)
  {
    this.message = message;
  }

  public String getMessage()
  {
    return message;
  }

  public void setMessage(String message)
  {
    this.message = message;
  }

  public int getXCoordinate()
  {
    return xCoordinate;
  }

  public void setXCoordinate(int x)
  {
    this.xCoordinate = x;
  }

  public int getYCoordinate()
  {
    return yCoordinate;
  }

  public void setYCoordinate(int y)
  {
    this.yCoordinate = y;
  }

  public boolean isCentered()
  {
    return centered;
  }

  public void setCentered(boolean centered)
  {
    this.centered = centered;
  }

  public void paintComponent(Graphics g)
  {
    super.paintComponent(g);

    if (centered)
    {
      // Get font metrics for the current font
      FontMetrics fm = g.getFontMetrics();

      // Find the center location to display
      int w = fm.stringWidth(message);  // Get the string width
      int h = fm.getAscent(); // Get the string height
      xCoordinate = (getWidth()-w)/2;
      yCoordinate = (getHeight()+h)/2;
    }

    g.drawString(message, xCoordinate, yCoordinate);
  }

  public Dimension getPreferredSize()
  {
    return new Dimension(200, 100);
  }

  public Dimension getMinimumSize()
  {
    return new Dimension(200, 100);
  }
}