第17章 项目

本章包含了一系列项目，它们都以本书介绍的内容为基础，并对早期的章节进行了一定程度的扩充。
与以前经历过的项目相比，这儿的大多数项目都明显要复杂得多，它们充分演示了新技术以及类库的运用。

17.1 文字处理
如果您有C或C++的经验，那么最开始可能会对Java控制文本的能力感到怀疑。事实上，我们最害怕的就是速度特别慢，这可能妨碍我们创造能力的发挥。然而，Java对应的工具（特别是String类）具有很强的功能，就象本节的例子展示的那样（而且性能也有一定程度的提升）。
正如大家即将看到的那样，建立这些例子的目的都是为了解决本书编制过程中遇到的一些问题。但是，它们的能力并非仅止于此。通过简单的改造，即可让它们在其他场合大显身手。除此以外，它们还揭示出了本书以前没有强调过的一项Java特性。

17.1.1 提取代码列表
对于本书每一个完整的代码列表（不是代码段），大家无疑会注意到它们都用特殊的注释记号起始与结束（'//:'和'///:~'）。之所以要包括这种标志信息，是为了能将代码从本书自动提取到兼容的源码文件中。在我的前一本书里，我设计了一个系统，可将测试过的代码文件自动合并到书中。但对于这本书，我发现一种更简便的做法是一旦通过了最初的测试，就把代码粘贴到书中。而且由于很难第一次就编译通过，所以我在书的内部编辑代码。但如何提取并测试代码呢？这个程序就是关键。如果你打算解决一个文字处理的问题，那么它也很有利用价值。该例也演示了String类的许多特性。
我首先将整本书都以ASCII文本格式保存成一个独立的文件。CodePackager程序有两种运行模式（在usageString有相应的描述）：如果使用-p标志，程序就会检查一个包含了ASCII文本（即本书的内容）的一个输入文件。它会遍历这个文件，按照注释记号提取出代码，并用位于第一行的文件名来决定创建文件使用什么名字。除此以外，在需要将文件置入一个特殊目录的时候，它还会检查package语句（根据由package语句指定的路径选择）。
但这样还不够。程序还要对包（package）名进行跟踪，从而监视章内发生的变化。由于每一章使用的所有包都以c02，c03，c04等等起头，用于标记它们所属的是哪一章（除那些以com起头的以外，它们在对不同的章进行跟踪的时候会被忽略）——只要每一章的第一个代码列表包含了一个package，所以CodePackager程序能知道每一章发生的变化，并将后续的文件放到新的子目录里。
每个文件提取出来时，都会置入一个SourceCodeFile对象，随后再将那个对象置入一个集合（后面还会详尽讲述这个过程）。这些SourceCodeFile对象可以简单地保存在文件中，那正是本项目的第二个用途。如果直接调用CodePackager，不添加-p标志，它就会将一个“打包”文件作为输入。那个文件随后会被提取（释放）进入单独的文件。所以-p标志的意思就是提取出来的文件已被“打包”（packed）进入这个单一的文件。
但为什么还要如此麻烦地使用打包文件呢？这是由于不同的计算机平台用不同的方式在文件里保存文本信息。其中最大的问题是换行字符的表示方法；当然，还有可能存在另一些问题。然而，Java有一种特殊类型的IO数据流——DataOutputStream——它可以保证“无论数据来自何种机器，只要使用一个DataInputStream收取这些数据，就可用本机正确的格式保存它们”。也就是说，Java负责控制与不同平台有关的所有细节，而这正是Java最具魅力的一点。所以-p标志能将所有东西都保存到单一的文件里，并采用通用的格式。用户可从Web下载这个文件以及Java程序，然后对这个文件运行CodePackager，同时不指定-p标志，文件便会释放到系统中正确的场所（亦可指定另一个子目录；否则就在当前目录创建子目录）。为确保不会留下与特定平台有关的格式，凡是需要描述一个文件或路径的时候，我们就使用File对象。除此以外，还有一项特别的安全措施：在每个子目录里都放入一个空文件；那个文件的名字指出在那个子目录里应找到多少个文件。
下面是完整的代码，后面会对它进行详细的说明：

//: CodePackager.java
// "Packs" and "unpacks" the code in "Thinking 
// in Java" for cross-platform distribution.
/* Commented so CodePackager sees it and starts
   a new chapter directory, but so you don't 
   have to worry about the directory where this
   program lives:
package c17;
*/
import java.util.*;
import java.io.*;

class Pr {
  static void error(String e) {
    System.err.println("ERROR: " + e);
    System.exit(1);
  }
}

class IO {
  static BufferedReader disOpen(File f) {
    BufferedReader in = null;
    try {
      in = new BufferedReader(
        new FileReader(f));
    } catch(IOException e) {
      Pr.error("could not open " + f);
    }
    return in;
  }
  static BufferedReader disOpen(String fname) {
    return disOpen(new File(fname));
  }
  static DataOutputStream dosOpen(File f) {
    DataOutputStream in = null;
    try {
      in = new DataOutputStream(
        new BufferedOutputStream(
          new FileOutputStream(f)));
    } catch(IOException e) {
      Pr.error("could not open " + f);
    }
    return in;
  }
  static DataOutputStream dosOpen(String fname) {
    return dosOpen(new File(fname));
  }
  static PrintWriter psOpen(File f) {
    PrintWriter in = null;
    try {
      in = new PrintWriter(
        new BufferedWriter(
          new FileWriter(f)));
    } catch(IOException e) {
      Pr.error("could not open " + f);
    }
    return in;
  }
  static PrintWriter psOpen(String fname) {
    return psOpen(new File(fname));
  }
  static void close(Writer os) {
    try {
      os.close();
    } catch(IOException e) {
      Pr.error("closing " + os);
    }
  }
  static void close(DataOutputStream os) {
    try {
      os.close();
    } catch(IOException e) {
      Pr.error("closing " + os);
    }
  }
  static void close(Reader os) {
    try {
      os.close();
    } catch(IOException e) {
      Pr.error("closing " + os);
    }
  }
}

class SourceCodeFile {
  public static final String 
    startMarker = "//:", // Start of source file
    endMarker = "} ///:~", // End of source
    endMarker2 = "}; ///:~", // C++ file end
    beginContinue = "} ///:Continued",
    endContinue = "///:Continuing",
    packMarker = "###", // Packed file header tag
    eol = // Line separator on current system
      System.getProperty("line.separator"),
    filesep = // System's file path separator
      System.getProperty("file.separator");
  public static String copyright = "";
  static {
    try {
      BufferedReader cr =
        new BufferedReader(
          new FileReader("Copyright.txt"));
      String crin;
      while((crin = cr.readLine()) != null)
        copyright += crin + "\n";
      cr.close();
    } catch(Exception e) {
      copyright = "";
    }
  }
  private String filename, dirname,
    contents = new String();
  private static String chapter = "c02";
  // The file name separator from the old system:
  public static String oldsep;
  public String toString() {
    return dirname + filesep + filename;
  }
  // Constructor for parsing from document file:
  public SourceCodeFile(String firstLine, 
      BufferedReader in) {
    dirname = chapter;
    // Skip past marker:
    filename = firstLine.substring(
        startMarker.length()).trim();
    // Find space that terminates file name:
    if(filename.indexOf(' ') != -1)
      filename = filename.substring(
          0, filename.indexOf(' '));
    System.out.println("found: " + filename);
    contents = firstLine + eol;
    if(copyright.length() != 0)
      contents += copyright + eol;
    String s;
    boolean foundEndMarker = false;
    try {
      while((s = in.readLine()) != null) {
        if(s.startsWith(startMarker))
          Pr.error("No end of file marker for " +
            filename);
        // For this program, no spaces before 
        // the "package" keyword are allowed
        // in the input source code:
        else if(s.startsWith("package")) {
          // Extract package name:
          String pdir = s.substring(
            s.indexOf(' ')).trim();
          pdir = pdir.substring(
            0, pdir.indexOf(';')).trim();
          // Capture the chapter from the package
          // ignoring the 'com' subdirectories:
          if(!pdir.startsWith("com")) {
            int firstDot = pdir.indexOf('.');
            if(firstDot != -1)
              chapter = 
                pdir.substring(0,firstDot);
            else
              chapter = pdir;
          }
          // Convert package name to path name:
          pdir = pdir.replace(
            '.', filesep.charAt(0));
          System.out.println("package " + pdir);
          dirname = pdir;
        }
        contents += s + eol;
        // Move past continuations:
        if(s.startsWith(beginContinue))
          while((s = in.readLine()) != null)
            if(s.startsWith(endContinue)) {
              contents += s + eol;
              break;
            }
        // Watch for end of code listing:
        if(s.startsWith(endMarker) ||
           s.startsWith(endMarker2)) {
          foundEndMarker = true;
          break;
        }
      }
      if(!foundEndMarker)
        Pr.error(
          "End marker not found before EOF");
      System.out.println("Chapter: " + chapter);
    } catch(IOException e) {
      Pr.error("Error reading line");
    }
  }
  // For recovering from a packed file:
  public SourceCodeFile(BufferedReader pFile) {
    try {
      String s = pFile.readLine();
      if(s == null) return;
      if(!s.startsWith(packMarker))
        Pr.error("Can't find " + packMarker
          + " in " + s);
      s = s.substring(
        packMarker.length()).trim();
      dirname = s.substring(0, s.indexOf('#'));
      filename = s.substring(s.indexOf('#') + 1);
      dirname = dirname.replace(
        oldsep.charAt(0), filesep.charAt(0));
      filename = filename.replace(
        oldsep.charAt(0), filesep.charAt(0));
      System.out.println("listing: " + dirname 
        + filesep + filename);
      while((s = pFile.readLine()) != null) {
        // Watch for end of code listing:
        if(s.startsWith(endMarker) ||
           s.startsWith(endMarker2)) {
          contents += s;
          break;
        }
        contents += s + eol;
      }
    } catch(IOException e) {
      System.err.println("Error reading line");
    }
  }
  public boolean hasFile() { 
    return filename != null; 
  }
  public String directory() { return dirname; }
  public String filename() { return filename; }
  public String contents() { return contents; }
  // To write to a packed file:
  public void writePacked(DataOutputStream out) {
    try {
      out.writeBytes(
        packMarker + dirname + "#" 
        + filename + eol);
      out.writeBytes(contents);
    } catch(IOException e) {
      Pr.error("writing " + dirname + 
        filesep + filename);
    }
  }
  // To generate the actual file:
  public void writeFile(String rootpath) {
    File path = new File(rootpath, dirname);
    path.mkdirs();
    PrintWriter p =
      IO.psOpen(new File(path, filename));
    p.print(contents);
    IO.close(p);
  }
}

class DirMap {
  private Hashtable t = new Hashtable();
  private String rootpath;
  DirMap() {
    rootpath = System.getProperty("user.dir");
  }
  DirMap(String alternateDir) {
    rootpath = alternateDir;
  }
  public void add(SourceCodeFile f){
    String path = f.directory();
    if(!t.containsKey(path))
      t.put(path, new Vector());
    ((Vector)t.get(path)).addElement(f);
  }
  public void writePackedFile(String fname) {
    DataOutputStream packed = IO.dosOpen(fname);
    try {
      packed.writeBytes("###Old Separator:" +
        SourceCodeFile.filesep + "###\n");
    } catch(IOException e) {
      Pr.error("Writing separator to " + fname);
    }
    Enumeration e = t.keys();
    while(e.hasMoreElements()) {
      String dir = (String)e.nextElement();
      System.out.println(
        "Writing directory " + dir);
      Vector v = (Vector)t.get(dir);
      for(int i = 0; i < v.size(); i++) {
        SourceCodeFile f = 
          (SourceCodeFile)v.elementAt(i);
        f.writePacked(packed);
      }
    }
    IO.close(packed);
  }
  // Write all the files in their directories:
  public void write() {
    Enumeration e = t.keys();
    while(e.hasMoreElements()) {
      String dir = (String)e.nextElement();
      Vector v = (Vector)t.get(dir);
      for(int i = 0; i < v.size(); i++) {
        SourceCodeFile f = 
          (SourceCodeFile)v.elementAt(i);
        f.writeFile(rootpath);
      }
      // Add file indicating file quantity
      // written to this directory as a check:
      IO.close(IO.dosOpen(
        new File(new File(rootpath, dir),
          Integer.toString(v.size())+".files")));
    }
  }
}

public class CodePackager {
  private static final String usageString =
  "usage: java CodePackager packedFileName" +
  "\nExtracts source code files from packed \n" +
  "version of Tjava.doc sources into " +
  "directories off current directory\n" +
  "java CodePackager packedFileName newDir\n" +
  "Extracts into directories off newDir\n" +
  "java CodePackager -p source.txt packedFile" +
  "\nCreates packed version of source files" +
  "\nfrom text version of Tjava.doc";
  private static void usage() {
    System.err.println(usageString);
    System.exit(1);
  }
  public static void main(String[] args) {
    if(args.length == 0) usage();
    if(args[0].equals("-p")) {
      if(args.length != 3)
        usage();
      createPackedFile(args);
    }
    else {
      if(args.length > 2)
        usage();
      extractPackedFile(args);
    }
  }
  private static String currentLine; 
  private static BufferedReader in;
  private static DirMap dm;
  private static void 
  createPackedFile(String[] args) {
    dm = new DirMap();
    in = IO.disOpen(args[1]);
    try {
      while((currentLine = in.readLine()) 
          != null) {
        if(currentLine.startsWith(
            SourceCodeFile.startMarker)) {
          dm.add(new SourceCodeFile(
                   currentLine, in));
        }
        else if(currentLine.startsWith(
            SourceCodeFile.endMarker))
          Pr.error("file has no start marker");
        // Else ignore the input line
      }
    } catch(IOException e) {
      Pr.error("Error reading " + args[1]);
    }
    IO.close(in);
    dm.writePackedFile(args[2]);
  }
  private static void 
  extractPackedFile(String[] args) {
    if(args.length == 2) // Alternate directory
      dm = new DirMap(args[1]);
    else // Current directory
      dm = new DirMap();
    in = IO.disOpen(args[0]);
    String s = null;
    try {
       s = in.readLine();
    } catch(IOException e) {
      Pr.error("Cannot read from " + in);
    }
    // Capture the separator used in the system
    // that packed the file:
    if(s.indexOf("###Old Separator:") != -1 ) {
      String oldsep = s.substring(
        "###Old Separator:".length());
      oldsep = oldsep.substring(
        0, oldsep. indexOf('#'));
      SourceCodeFile.oldsep = oldsep;
    }
    SourceCodeFile sf = new SourceCodeFile(in);
    while(sf.hasFile()) {
      dm.add(sf);
      sf = new SourceCodeFile(in);
    }
    dm.write();
  }
} ///:~

//////////////////////////////////////////////////
// Copyright (c) Bruce Eckel, 1998
// Source code file from the book "Thinking in Java"
// All rights reserved EXCEPT as allowed by the
// following statements: You may freely use this file
// for your own work (personal or commercial),
// including modifications and distribution in
// executable form only. Permission is granted to use
// this file in classroom situations, including its
// use in presentation materials, as long as the book
// "Thinking in Java" is cited as the source. 
// Except in classroom situations, you may not copy
// and distribute this code; instead, the sole
// distribution point is http://www.BruceEckel.com 
// (and official mirror sites) where it is
// freely available. You may not remove this
// copyright and notice. You may not distribute
// modified versions of the source code in this
// package. You may not use this file in printed
// media without the express permission of the
// author. Bruce Eckel makes no representation about
// the suitability of this software for any purpose.
// It is provided "as is" without express or implied
// warranty of any kind, including any implied
// warranty of merchantability, fitness for a
// particular purpose or non-infringement. The entire
// risk as to the quality and performance of the
// software is with you. Bruce Eckel and the
// publisher shall not be liable for any damages
// suffered by you or any third party as a result of
// using or distributing software. In no event will
// Bruce Eckel or the publisher be liable for any
// lost revenue, profit, or data, or for direct,
// indirect, special, consequential, incidental, or
// punitive damages, however caused and regardless of
// the theory of liability, arising out of the use of
// or inability to use software, even if Bruce Eckel
// and the publisher have been advised of the
// possibility of such damages. Should the software
// prove defective, you assume the cost of all
// necessary servicing, repair, or correction. If you
// think you've found an error, please email all
// modified files with clearly commented changes to:
// Bruce@EckelObjects.com. (please use the same
// address for non-code errors found in the book).
//////////////////////////////////////////////////

//: ClassScanner.java
// Scans all files in directory for classes
// and identifiers, to check capitalization.
// Assumes properly compiling code listings.
// Doesn't do everything right, but is a very
// useful aid.
import java.io.*;
import java.util.*;

class MultiStringMap extends Hashtable {
  public void add(String key, String value) {
    if(!containsKey(key))
      put(key, new Vector());
    ((Vector)get(key)).addElement(value);
  }
  public Vector getVector(String key) {
    if(!containsKey(key)) {
      System.err.println(
        "ERROR: can't find key: " + key);
      System.exit(1);
    }
    return (Vector)get(key);
  }
  public void printValues(PrintStream p) {
    Enumeration k = keys();
    while(k.hasMoreElements()) {
      String oneKey = (String)k.nextElement();
      Vector val = getVector(oneKey);
      for(int i = 0; i < val.size(); i++)
        p.println((String)val.elementAt(i));
    }
  }
}

public class ClassScanner {
  private File path;
  private String[] fileList;
  private Properties classes = new Properties();
  private MultiStringMap 
    classMap = new MultiStringMap(),
    identMap = new MultiStringMap();
  private StreamTokenizer in;
  public ClassScanner() {
    path = new File(".");
    fileList = path.list(new JavaFilter());
    for(int i = 0; i < fileList.length; i++) {
      System.out.println(fileList[i]);
      scanListing(fileList[i]);
    }
  }
  void scanListing(String fname) {
    try {
      in = new StreamTokenizer(
          new BufferedReader(
            new FileReader(fname)));
      // Doesn't seem to work:
      // in.slashStarComments(true);
      // in.slashSlashComments(true);
      in.ordinaryChar('/');
      in.ordinaryChar('.');
      in.wordChars('_', '_');
      in.eolIsSignificant(true);
      while(in.nextToken() != 
            StreamTokenizer.TT_EOF) {
        if(in.ttype == '/')
          eatComments();
        else if(in.ttype == 
                StreamTokenizer.TT_WORD) {
          if(in.sval.equals("class") || 
             in.sval.equals("interface")) {
            // Get class name:
               while(in.nextToken() != 
                     StreamTokenizer.TT_EOF
                     && in.ttype != 
                     StreamTokenizer.TT_WORD)
                 ;
               classes.put(in.sval, in.sval);
               classMap.add(fname, in.sval);
          }
          if(in.sval.equals("import") ||
             in.sval.equals("package"))
            discardLine();
          else // It's an identifier or keyword
            identMap.add(fname, in.sval);
        }
      }
    } catch(IOException e) {
      e.printStackTrace();
    }
  }
  void discardLine() {
    try {
      while(in.nextToken() != 
            StreamTokenizer.TT_EOF
            && in.ttype != 
            StreamTokenizer.TT_EOL)
        ; // Throw away tokens to end of line
    } catch(IOException e) {
      e.printStackTrace();
    }
  }
  // StreamTokenizer's comment removal seemed
  // to be broken. This extracts them:
  void eatComments() {
    try {
      if(in.nextToken() != 
         StreamTokenizer.TT_EOF) {
        if(in.ttype == '/')
          discardLine();
        else if(in.ttype != '*')
          in.pushBack();
        else 
          while(true) {
            if(in.nextToken() == 
              StreamTokenizer.TT_EOF)
              break;
            if(in.ttype == '*')
              if(in.nextToken() != 
                StreamTokenizer.TT_EOF
                && in.ttype == '/')
                break;
          }
      }
    } catch(IOException e) {
      e.printStackTrace();
    }
  }
  public String[] classNames() {
    String[] result = new String[classes.size()];
    Enumeration e = classes.keys();
    int i = 0;
    while(e.hasMoreElements())
      result[i++] = (String)e.nextElement();
    return result;
  }
  public void checkClassNames() {
    Enumeration files = classMap.keys();
    while(files.hasMoreElements()) {
      String file = (String)files.nextElement();
      Vector cls = classMap.getVector(file);
      for(int i = 0; i < cls.size(); i++) {
        String className = 
          (String)cls.elementAt(i);
        if(Character.isLowerCase(
             className.charAt(0)))
          System.out.println(
            "class capitalization error, file: "
            + file + ", class: " 
            + className);
      }
    }
  }
  public void checkIdentNames() {
    Enumeration files = identMap.keys();
    Vector reportSet = new Vector();
    while(files.hasMoreElements()) {
      String file = (String)files.nextElement();
      Vector ids = identMap.getVector(file);
      for(int i = 0; i < ids.size(); i++) {
        String id = 
          (String)ids.elementAt(i);
        if(!classes.contains(id)) {
          // Ignore identifiers of length 3 or
          // longer that are all uppercase
          // (probably static final values):
          if(id.length() >= 3 &&
             id.equals(
               id.toUpperCase()))
            continue;
          // Check to see if first char is upper:
          if(Character.isUpperCase(id.charAt(0))){
            if(reportSet.indexOf(file + id)
                == -1){ // Not reported yet
              reportSet.addElement(file + id);
              System.out.println(
                "Ident capitalization error in:"
                + file + ", ident: " + id);
            }
          }
        }
      }
    }
  }
  static final String usage =
    "Usage: \n" + 
    "ClassScanner classnames -a\n" +
    "\tAdds all the class names in this \n" +
    "\tdirectory to the repository file \n" +
    "\tcalled 'classnames'\n" +
    "ClassScanner classnames\n" +
    "\tChecks all the java files in this \n" +
    "\tdirectory for capitalization errors, \n" +
    "\tusing the repository file 'classnames'";
  private static void usage() {
    System.err.println(usage);
    System.exit(1);
  }
  public static void main(String[] args) {
    if(args.length < 1 || args.length > 2)
      usage();
    ClassScanner c = new ClassScanner();
    File old = new File(args[0]);
    if(old.exists()) {
      try {
        // Try to open an existing 
        // properties file:
        InputStream oldlist =
          new BufferedInputStream(
            new FileInputStream(old));
        c.classes.load(oldlist);
        oldlist.close();
      } catch(IOException e) {
        System.err.println("Could not open "
          + old + " for reading");
        System.exit(1);
      }
    }
    if(args.length == 1) {
      c.checkClassNames();
      c.checkIdentNames();
    }
    // Write the class names to a repository:
    if(args.length == 2) {
      if(!args[1].equals("-a"))
        usage();
      try {
        BufferedOutputStream out =
          new BufferedOutputStream(
            new FileOutputStream(args[0]));
        c.classes.save(out,
          "Classes found by ClassScanner.java");
        out.close();
      } catch(IOException e) {
        System.err.println(
          "Could not write " + args[0]);
        System.exit(1);
      }
    }
  }
}

class JavaFilter implements FilenameFilter {
  public boolean accept(File dir, String name) {
    // Strip path information:
    String f = new File(name).getName();
    return f.trim().endsWith(".java");
  }
} ///:~

//: DisplayMethods.java
// Display the methods of any class inside
// a window. Dynamically narrows your search.
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import java.lang.reflect.*;
import java.io.*;

public class DisplayMethods extends Applet {
  Class cl;
  Method[] m;
  Constructor[] ctor;
  String[] n = new String[0];
  TextField 
    name = new TextField(40),
    searchFor = new TextField(30);
  Checkbox strip = 
    new Checkbox("Strip Qualifiers");
  TextArea results = new TextArea(40, 65);
  public void init() {
    strip.setState(true);
    name.addTextListener(new NameL());
    searchFor.addTextListener(new SearchForL());
    strip.addItemListener(new StripL());
    Panel 
      top = new Panel(),
      lower = new Panel(),
      p = new Panel();
    top.add(new Label("Qualified class name:"));
    top.add(name);
    lower.add(
      new Label("String to search for:"));
    lower.add(searchFor);
    lower.add(strip);
    p.setLayout(new BorderLayout());
    p.add(top, BorderLayout.NORTH);
    p.add(lower, BorderLayout.SOUTH);
    setLayout(new BorderLayout());
    add(p, BorderLayout.NORTH);
    add(results, BorderLayout.CENTER);
  }
  class NameL implements TextListener {
    public void textValueChanged(TextEvent e) {
      String nm = name.getText().trim();
      if(nm.length() == 0) {
        results.setText("No match");
        n = new String[0];
        return;
      }
      try {
        cl = Class.forName(nm);
      } catch (ClassNotFoundException ex) {
        results.setText("No match");
        return;
      }
      m = cl.getMethods();
      ctor = cl.getConstructors();
      // Convert to an array of Strings:
      n = new String[m.length + ctor.length];
      for(int i = 0; i < m.length; i++)
        n[i] = m[i].toString();
      for(int i = 0; i < ctor.length; i++)
        n[i + m.length] = ctor[i].toString();
      reDisplay();
    }
  }
  void reDisplay() {
    // Create the result set:
    String[] rs = new String[n.length];
    String find = searchFor.getText();
    int j = 0;
    // Select from the list if find exists:
    for (int i = 0; i < n.length; i++) {
      if(find == null)
        rs[j++] = n[i];
      else if(n[i].indexOf(find) != -1)
          rs[j++] = n[i];
    }
    results.setText("");
    if(strip.getState() == true)
      for (int i = 0; i < j; i++)
        results.append(
          StripQualifiers.strip(rs[i]) + "\n");
    else // Leave qualifiers on
      for (int i = 0; i < j; i++)
        results.append(rs[i] + "\n");
  }
  class StripL implements ItemListener {
    public void itemStateChanged(ItemEvent e) {
      reDisplay();
    }
  }
  class SearchForL implements TextListener {
    public void textValueChanged(TextEvent e) {
      reDisplay();
    }
  }
  public static void main(String[] args) {
    DisplayMethods applet = new DisplayMethods();
    Frame aFrame = new Frame("Display Methods");
    aFrame.addWindowListener(
      new WindowAdapter() {
        public void windowClosing(WindowEvent e) {
          System.exit(0);
        }
      });
    aFrame.add(applet, BorderLayout.CENTER);
    aFrame.setSize(500,750);
    applet.init();
    applet.start();
    aFrame.setVisible(true);
  }
}

class StripQualifiers {
  private StreamTokenizer st;
  public StripQualifiers(String qualified) {
      st = new StreamTokenizer(
        new StringReader(qualified));
      st.ordinaryChar(' ');
  }
  public String getNext() {
    String s = null;
    try {
      if(st.nextToken() !=
            StreamTokenizer.TT_EOF) {
        switch(st.ttype) {
          case StreamTokenizer.TT_EOL:
            s = null;
            break;
          case StreamTokenizer.TT_NUMBER:
            s = Double.toString(st.nval);
            break;
          case StreamTokenizer.TT_WORD:
            s = new String(st.sval);
            break;
          default: // single character in ttype
            s = String.valueOf((char)st.ttype);
        }
      }
    } catch(IOException e) {
      System.out.println(e);
    }
    return s;
  }
  public static String strip(String qualified) {
    StripQualifiers sq = 
      new StripQualifiers(qualified);
    String s = "", si;
    while((si = sq.getNext()) != null) {
      int lastDot = si.lastIndexOf('.');
      if(lastDot != -1)
        si = si.substring(lastDot + 1);
      s += si;
    }
    return s;
  }
} ///:~

//: FieldOBeasts.java
// Demonstration of complexity theory; simulates 
// herding behavior in animals. Adapted from
// a program by Larry O'Brien lobrien@msn.com
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import java.util.*;

class Beast {
  int
    x, y,            // Screen position
    currentSpeed;    // Pixels per second
  float currentDirection;  // Radians
  Color color;      // Fill color
  FieldOBeasts field; // Where the Beast roams
  static final int GSIZE = 10; // Graphic size

  public Beast(FieldOBeasts f, int x, int y, 
      float cD, int cS, Color c) {
    field = f;
    this.x = x;
    this.y = y;
    currentDirection = cD;
    currentSpeed = cS;
    color = c;
  }
  public void step() {
    // You move based on those within your sight:
    Vector seen = field.beastListInSector(this);
    // If you're not out in front
    if(seen.size() > 0) {
      // Gather data on those you see
      int totalSpeed = 0;
      float totalBearing = 0.0f;
      float distanceToNearest = 100000.0f;
      Beast nearestBeast = 
        (Beast)seen.elementAt(0);
      Enumeration e = seen.elements();
      while(e.hasMoreElements()) {
        Beast aBeast = (Beast) e.nextElement();
        totalSpeed += aBeast.currentSpeed;
        float bearing = 
          aBeast.bearingFromPointAlongAxis(
            x, y, currentDirection);
        totalBearing += bearing;
        float distanceToBeast = 
          aBeast.distanceFromPoint(x, y);
        if(distanceToBeast < distanceToNearest) {
          nearestBeast = aBeast;
          distanceToNearest = distanceToBeast;
        }
      }
      // Rule 1: Match average speed of those 
      // in the list:
      currentSpeed = totalSpeed / seen.size();
      // Rule 2: Move towards the perceived
      // center of gravity of the herd:
      currentDirection = 
        totalBearing / seen.size();
      // Rule 3: Maintain a minimum distance 
      // from those around you:
      if(distanceToNearest <= 
         field.minimumDistance) {
        currentDirection = 
          nearestBeast.currentDirection;
        currentSpeed = nearestBeast.currentSpeed;
        if(currentSpeed > field.maxSpeed) {
          currentSpeed = field.maxSpeed;
        }
      }
    } 
    else {  // You are in front, so slow down
      currentSpeed = 
        (int)(currentSpeed * field.decayRate);
    }
    // Make the beast move:
    x += (int)(Math.cos(currentDirection) 
               * currentSpeed);
    y += (int)(Math.sin(currentDirection)
               * currentSpeed);
    x %= field.xExtent;
    y %= field.yExtent;
    if(x < 0)
      x += field.xExtent;
    if(y < 0)
      y += field.yExtent;
  }
  public float bearingFromPointAlongAxis (
      int originX, int originY, float axis) {
    // Returns bearing angle of the current Beast
    // in the world coordiante system
    try {
      double bearingInRadians = 
        Math.atan(
          (this.y - originY) / 
          (this.x - originX));
      // Inverse tan has two solutions, so you 
      // have to correct for other quarters:
      if(x < originX) {  
        if(y < originY) {
          bearingInRadians += - (float)Math.PI;
        } 
        else {
          bearingInRadians = 
            (float)Math.PI - bearingInRadians;
        }
      }
      // Just subtract the axis (in radians):
      return (float) (axis - bearingInRadians);
    } catch(ArithmeticException aE) {
      // Divide by 0 error possible on this
      if(x > originX) {
          return 0;
      } 
      else
        return (float) Math.PI;
    }
  }
  public float distanceFromPoint(int x1, int y1){
    return (float) Math.sqrt(
      Math.pow(x1 - x, 2) + 
      Math.pow(y1 - y, 2));
  }
  public Point position() { 
    return new Point(x, y);
  }
  // Beasts know how to draw themselves:
  public void draw(Graphics g) {
    g.setColor(color);
    int directionInDegrees = (int)(
      (currentDirection * 360) / (2 * Math.PI));
    int startAngle = directionInDegrees - 
      FieldOBeasts.halfFieldOfView;
    int endAngle = 90;
    g.fillArc(x, y, GSIZE, GSIZE, 
      startAngle, endAngle);
  }
}

public class FieldOBeasts extends Applet 
    implements Runnable {
  private Vector beasts;
  static float 
    fieldOfView = 
      (float) (Math.PI / 4), // In radians
    // Deceleration % per second:
    decayRate = 1.0f, 
    minimumDistance = 10f; // In pixels
  static int
    halfFieldOfView = (int)(
      (fieldOfView * 360) / (2 * Math.PI)),
    xExtent = 0,
    yExtent = 0,
    numBeasts = 50,
    maxSpeed = 20; // Pixels/second
  boolean uniqueColors = true;
  Thread thisThread;
  int delay = 25;
  public void init() {
    if (xExtent == 0 && yExtent == 0) {
      xExtent = Integer.parseInt(
        getParameter("xExtent"));
      yExtent = Integer.parseInt(
        getParameter("yExtent"));
    }
    beasts = 
      makeBeastVector(numBeasts, uniqueColors);
    // Now start the beasts a-rovin':
    thisThread = new Thread(this);
    thisThread.start();
  }
  public void run() {
    while(true) {
      for(int i = 0; i < beasts.size(); i++){
        Beast b = (Beast) beasts.elementAt(i);
        b.step();
      }
      try {
        thisThread.sleep(delay);
      } catch(InterruptedException ex){}
      repaint(); // Otherwise it won't update
    }
  }
  Vector makeBeastVector(
      int quantity, boolean uniqueColors) {
    Vector newBeasts = new Vector();
    Random generator = new Random();
    // Used only if uniqueColors is on:
    double cubeRootOfBeastNumber = 
      Math.pow((double)numBeasts, 1.0 / 3.0);
    float colorCubeStepSize = 
      (float) (1.0 / cubeRootOfBeastNumber);
    float r = 0.0f;
    float g = 0.0f;
    float b = 0.0f;
    for(int i = 0; i < quantity; i++) {
      int x = 
        (int) (generator.nextFloat() * xExtent);
      if(x > xExtent - Beast.GSIZE) 
        x -= Beast.GSIZE;
      int y = 
        (int) (generator.nextFloat() * yExtent);
      if(y > yExtent - Beast.GSIZE) 
        y -= Beast.GSIZE;
      float direction = (float)(
        generator.nextFloat() * 2 * Math.PI);
      int speed = (int)(
        generator.nextFloat() * (float)maxSpeed);
      if(uniqueColors) {
        r += colorCubeStepSize;
        if(r > 1.0) {
          r -= 1.0f;
          g += colorCubeStepSize;
          if( g > 1.0) {
            g -= 1.0f;
            b += colorCubeStepSize;
            if(b > 1.0) 
              b -= 1.0f;
          }
        }
      }
      newBeasts.addElement(
        new Beast(this, x, y, direction, speed, 
          new Color(r,g,b)));
    }
    return newBeasts;
  }
  public Vector beastListInSector(Beast viewer) {
    Vector output = new Vector();
    Enumeration e = beasts.elements();
    Beast aBeast = (Beast)beasts.elementAt(0);
    int counter = 0;
    while(e.hasMoreElements()) {
      aBeast = (Beast) e.nextElement();
      if(aBeast != viewer) {
        Point p = aBeast.position();
        Point v = viewer.position();
        float bearing = 
          aBeast.bearingFromPointAlongAxis(
            v.x, v.y, viewer.currentDirection);
        if(Math.abs(bearing) < fieldOfView / 2)
         output.addElement(aBeast);
      }
    }
    return output;
  }
  public void paint(Graphics g)  {
    Enumeration e = beasts.elements();
    while(e.hasMoreElements()) {
      ((Beast)e.nextElement()).draw(g);
    }
  }
  public static void main(String[] args)   {
    FieldOBeasts field = new FieldOBeasts();
    field.xExtent = 640;
    field.yExtent = 480;
    Frame frame = new Frame("Field 'O Beasts");
    // Optionally use a command-line argument
    // for the sleep time:
    if(args.length >= 1)
      field.delay = Integer.parseInt(args[0]);
    frame.addWindowListener(
      new WindowAdapter() {
        public void windowClosing(WindowEvent e) {
          System.exit(0);
        }
      });
    frame.add(field, BorderLayout.CENTER);
    frame.setSize(640,480);
    field.init();
    field.start();
    frame.setVisible(true);
  }
} ///:~

<applet
code=FieldOBeasts
width=640
height=480>
<param name=xExtent value = "640">
<param name=yExtent value = "480">
</applet>

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