treesap.java

Java经典例程 从外国一大学计算机教授出版物下载的代码 经典

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.util.*;

public class TreesAp extends Applet implements ActionListener {

  /* The Trees applet    by J M Bishop   January 1997
   * ================    Java 1.1 Jan 1998

     Asks for information about the leaves of a tree.
     Codes the information and links to a URL where

     further information about the tree is stored.
     Gets the tree names and codes from an HTML page.
     Illustrates interaction with a browser,
     button arrays, image tracking,
     nested panel layouts and string tokenizers.
  */

  // A TextField, boolean and integer for each leaf part.
  private TextField widthField, lengthField, messageField;
  private Button againButton;
  private boolean gotChoice = false;
  private boolean gotWidth = false;
  private boolean gotLength = false;
  private int c, w, l;

  private Hashtable table = new Hashtable ();

  private String patterns [] = {
    "Alternate", "Opposite",
    "Whorled",   "Palmate",
    "Complex",   "Bipinnate"};

  private Button patternButton [] = new Button[6];


  public void init () {
  //===================
    // First read in the parameters from the HTML page
       setUpTable();

    // Create the applet screen with two text fields above
    // and one below. In the centre is the grid of nine
    // leaf patterns, each a border panel in its own right
    // with a button in the south and a canvas occupying
    // the rest. The canvas is painted by the leafPattern
    // class. The font is set to 10pt.

    Font f = new Font ("SanSerif",Font.PLAIN,10);
    this.setFont (f);
    setLayout(new BorderLayout(0,0));
    Panel p = new Panel ();
      p.add (new Label ("Leaf width"));
      widthField = new TextField (8);
        p.add (widthField);
        widthField.addActionListener(this);
      p.add (new Label ("Leaf length"));
      lengthField = new TextField (8);
        p.add (lengthField);
        lengthField.addActionListener(this);
    add ("North",p);

    // Create a panel for the nine leaf patterns
    Panel q = new Panel ();
      q.setLayout(new GridLayout(2,3));
      for (int b = 0; b<patterns.length; b++) {
        Panel s = new Panel ();
          s.setLayout(new BorderLayout(0,0));
          s.add ("Center",new leafPattern (this,b));
          patternButton[b] = new Button(patterns[b]);
            patternButton[b].addActionListener(this);
            s.add ("South",patternButton[b]);
        q.add (s);
      }
    add ("Center",q);

    // Follow up with a message and again button
    // at the bottom of the applet.
    Panel r = new Panel();
      messageField = new TextField (30);
        r.add (messageField);
      againButton = new Button ("Again");
        r.add(againButton);
        againButton.addActionListener(this);
    add("South",r);
  }

  private void setUpTable() {
  //=========================
      String s, item;
      StringTokenizer t;
      int code;
      s = getParameter("entries");
      int n = Integer.parseInt(s);
      for (int i = 0; i<n; i++) {
      // extract a tree name from the html
        String tree = getParameter("tree-"+(i+1));
      // read all its codes
        s = getParameter("codes-"+(i+1));
        t = new StringTokenizer (s);
      // store each code-tree pair in the table.
        while (true) {
          try {
            item = t.nextToken();
            code = Integer.parseInt(item.trim());
            table.put(new Integer(code),tree);
          }
          catch (NoSuchElementException e) {
            break;
          }
        }
     }
  }

  public void actionPerformed (ActionEvent e) {
  //===========================================
    Object source = e.getSource();
    String name = e.getActionCommand();

    if (source == widthField) {
      w = readValue(widthField);
      gotWidth = true;
    } else if (source == lengthField) {
      l = readValue(lengthField);
      gotLength = true;
    } else if (source == againButton) {
       resetFields();
    } else if (name instanceof String) {
      c = 0;
      while (!name.equals(patterns[c])) c++;
      gotChoice = true;
      patternButton[c].setBackground(Color.green);
    }
    if (gotChoice & gotLength & gotWidth)
      findTree ();
  }

  private void findTree () {
  //========================
  // Calculate the three-part code
    int part2=convertLength();
    int part3=convertWidth();
    int code = 100*(c+1)+10*part2+part3;
  // Fetch the tree name from the table if it exists
    String tree = (String) table.get(new Integer (code));
    if (tree == null)
      setMessage("No information on code "+code+" yet.");
    else
      fetchTree (tree);
  }

  private void fetchTree (String treeName) {
  //====================================
  // Try to get a web page of information on
  // the tree.
    try {
     AppletContext context = getAppletContext ();
      String s = treeName+".html";
      setMessage("Looking for "+s);
      URL u = new URL (getCodeBase(),s);
      context.showDocument(u,"_self");
    }
    catch (MalformedURLException e) {
      setMessage("No information for that tree yet");
    }
  }

  // Code conversion methods
  //========================

  private int convertLength () {
  // returns a code based on the leaf length supplied
    if (l<=25) return 4; else
    if (l<=50) return 5; else
    if (l<=100) return 6; else
    if (l<=200) return 7; else
                return 8;
  }
  private int convertWidth () {
  // returns a code based on the leaf width supplied
    if (w<=10) return 4; else
    if (w<=20) return 5; else
    if (w<=40) return 6; else
    if (w<=80) return 7; else
               return 8;
  }

// Utility methods
  // ===============
  private int readValue (TextField t) {
      int x = Integer.parseInt(t.getText());
      t.setEditable(false);
      t.setBackground(Color.green);
      return x;
  }

  private void clearField(TextField t) {
    t.setEditable(true);
    t.setBackground(Color.white);
    t.setText("");
  }

  private void resetFields () {
    gotChoice = false;
    patternButton[c].setBackground(Color.lightGray);
    gotWidth = false;
    clearField(widthField);
    gotLength = false;
    clearField(lengthField);
    clearField(messageField);
    messageField.setEditable(false);
  }

  private void setMessage(String s) {
    messageField.setText(s);
    messageField.setBackground(Color.green);
  }

  class leafPattern extends Canvas {
  //================================
    Image im;

    leafPattern(Applet a, int b) {
      weAre = a;
    // Construct the URL name
      pattern = "images/leaf"+Integer.toString(b)+".jpg";
    // Get the image
      im = weAre.getImage(weAre.getCodeBase(),pattern);
    // Ensure that the image has been received before
    // the constructor returns.
      MediaTracker tracker = new MediaTracker(weAre);
      tracker.addImage(im, 0);
      try { tracker.waitForID(0);}
      catch (InterruptedException e) {}
    }

    public void paint (Graphics g) {
      g.drawImage(im,0,0,this);
    }

    private Applet weAre;
    private String pattern;
  }
}