exercise14_13.java

Introduction to java programming 一书中所有编程练习部分的源码

// Exercise14_13.java: Simulate elevators
/* Simulating elevator
Write a program to simulate an elevator going up
and down as shown in Figure 12.10. The buttons on the left
indicating the floor on which the rider is now.
The rider must first click a button on the left to request
the elevator move to the floor to pick up the rider.
When the rider gets inside the elevator, the rider clicks
the buttons on the right to request the elevator to go to
the specified floor.
*/

/*testing notes 10/5/97:
Testing synchronization: Pressing a button before the previous button
action ends.
The synchronization works fine on JDK using java or appletviewer.
It also works fine with jview, but not with IE4.0 Preview II.
*/

// Modified 3/19/2000

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

public class Exercise14_13 extends JApplet {
  private JLabel jlblStatue = new JLabel("Status");
  private Elevator elevator = new Elevator(this);

  public void init() {
    // Create left buttons and right buttons
    ButtonPanel lb = new ButtonPanel(elevator, true);
    ButtonPanel rb = new ButtonPanel(elevator, false);

    // Place status label on the north, left buttons on the west
    // right buttons on the east and the elevator on the center
    // Set applet layout
    getContentPane().setLayout(new BorderLayout());
    getContentPane().add(jlblStatue, BorderLayout.NORTH);
    getContentPane().add(lb, BorderLayout.WEST);
    getContentPane().add(elevator, BorderLayout.CENTER);
    getContentPane().add(rb, BorderLayout.EAST);
  }

  // Set status on the status label to indicate left or right buttons are at work
  public void setStatus(String status, Color color) {
    jlblStatue.setForeground(color);
    jlblStatue.setText(status);
  }

  // Enable the applet to run standalone
  // Main method
  public static void main(String[] args) {
    // Create a frame
    JFrame frame = new JFrame("Exercise14_13: Elevator Simulation");

    // Create an instance of the applet
    Exercise14_13 applet = new Exercise14_13();

    // Add the applet instance to the frame
    frame.getContentPane().add(applet, BorderLayout.CENTER);

    // Invoke init() and start()
    applet.init();
    applet.start();

    // Display the frame
    frame.setSize(200, 200);
    frame.setVisible(true);
  }
}

// The elevator class encapsulates elevator operations
class Elevator extends JPanel implements Runnable {
  private Exercise14_13 app;		// The applet
  private boolean left;			// Left or right button
  private int destinationFloor = 6;	// Elevator destination floor
  private int width = 30;  // Elevator width
  private int height = 30; // Elevator height
  private int x = 50;	// The x coordinator of the elevator's upper left corner
  private int currentY = height*6; // Elevator current location
  private int dy = 4; // Moving interval
  private Thread thread = null; // Run the while loop on a separate thread

  public Elevator(Exercise14_13 app) {
    this.app = app;	// Passed from applet
    setBackground(Color.yellow); // Set elevator background color
    thread = new Thread(this);		// Create thread
    thread.start();	// Move the elevator the initial location, i.e. the first floor
  }

  // Set elevator color
  public void setColor(Color color) {
    setForeground(color);
  }

  // Move the elevator to destination
  public void move(int toFloor, boolean left) {
    destinationFloor = toFloor;
    this.left = left;
    thread = new Thread(this);
    thread.start();
  }

  // Run the elevator to the destination, called from move()
  public synchronized void run() {
    //set status and set elevator color
    if (left) {
      app.setStatus("getting passengers", Color.black);
      this.setColor(Color.green);
    }
    else {
      app.setStatus("sending passengers", Color.red);
      this.setColor(Color.red);
    }

    //newY is the destination floor's y
    int newY = (8-destinationFloor)*height;

    if (newY < currentY) { //moving up
      while (currentY > newY) {
        try {
          thread.sleep(200);
	      }
	      catch (InterruptedException ex) {};
	      currentY = currentY - dy;
	      repaint();
      }
    }
    else  {  // moving down
      while (currentY < newY) {
        try {
          thread.sleep(200);
	      }
	      catch (InterruptedException ex) {};
	      currentY = currentY + dy;
	      repaint();
      }
    }
  }

  // Paint elevator
  public void paintComponent(Graphics g) {
    super.paintComponent(g);

    height = getSize().height/8;

    for (int i=0; i<9; i++) {
      g.drawLine(0, i*height, this.getSize().width, i*height);
    }

    g.fillRect(x, currentY, width, height);
  }
}

//The ButtonPanel encapsulates buttons
class ButtonPanel extends JPanel implements ActionListener {
  private Elevator elevator;	// The elevator
  private boolean left;		// Indicate left or right button
  private JButton b[] = new JButton[8];  // Buttons

  ButtonPanel(Elevator elevator, boolean left) {
    // Pass the elevator, frame, status to the button panel
    this.elevator = elevator;
    this.left = left;

    // Set panel layout
    setLayout(new GridLayout(8, 1, 0, 0));
    // Set panel background color
    setBackground(Color.blue);
    // Add buttons to the panel
    for (int i=8; i>0; i--)
      add(b[i-1] = new JButton("F"+(char)('0'+i)));

    // Register listeners
    for (int i=0; i<8; i++)
      b[i].addActionListener(this);
  }

  // Handle button actions
  public void actionPerformed(ActionEvent e) {
    String arg = e.getActionCommand(); // A label like "F8"
    if (e.getSource() instanceof JButton)
      elevator.move((int)arg.charAt(1)-48, left); // Ascii '0' is 48
  }
}