Listing 1. for method processChar
private void processChar(String str){
    char strChar = str.charAt(0);
    if (mode != this.COMMENT_MODE){
      mode = TEXT_MODE;
    }
      switch (strChar){
        case ('{'):case ('}'):case (' '): case('\n'):
        case ('('):case (')'):case (';'):case ('.'):{
          checkForKeyword();
          if (mode == STRING_MODE && strChar == '\n'){
            mode = TEXT_MODE;
          }
        }
        break;
        case ('"'):{
          insertTextString(str, currentPos);
          this.checkForString();
        }
        break;
        case ('0'):case ('1'):case ('2'):case ('3'):case ('4'):
        case ('5'):case ('6'):case ('7'):case ('8'):case ('9'):{
          checkForNumber();
        }
        break;
        case ('*'):case ('/'):{
          checkForComment();
        }
        break;
      }
      if (mode == this.TEXT_MODE){
        this.checkForString();
      }
      if (mode == this.STRING_MODE){
        insertTextString(str, this.currentPos);
      }
      else if (mode == this.NUMBER_MODE){
        insertNumberString(str, this.currentPos);
      }
      else if (mode == this.COMMENT_MODE){
        insertCommentString(str, this.currentPos);
      }
 

  }

Listing 2.
import com.sun.java.swing.*;
import java.util.*;

public class Test{

  public static void main(String[] args) {
    JFrame frame = new JFrame();
    JTextPane editor = new JTextPane();
    CodeDocument doc = new CodeDocument();
    Vector keywords = new Vector();
    keywords.addElement("abstract");
    keywords.addElement("boolean");
    keywords.addElement("break");
    keywords.addElement("byte");
    keywords.addElement("byvalue");
    keywords.addElement("case");
    keywords.addElement("cast");
    keywords.addElement("catch");
    keywords.addElement("char");
    keywords.addElement("class");
    keywords.addElement("const");
    keywords.addElement("continue");
    keywords.addElement("default");
    keywords.addElement("do");
    keywords.addElement("double");
    keywords.addElement("extends");
    keywords.addElement("else");
    keywords.addElement("false");
    keywords.addElement("final");
    keywords.addElement("finally");
    keywords.addElement("float");
    keywords.addElement("for");
    keywords.addElement("future");
    keywords.addElement("generic");
    keywords.addElement("if");
    keywords.addElement("implements");
    keywords.addElement("import");
    keywords.addElement("inner");
    keywords.addElement("instanceof");
    keywords.addElement("int");
    keywords.addElement("interface");
    keywords.addElement("long");
    keywords.addElement("native");
    keywords.addElement("new");
    keywords.addElement("null");
    keywords.addElement("operator");
    keywords.addElement("outer");
    keywords.addElement("package");
    keywords.addElement("private");
    keywords.addElement("protected");
    keywords.addElement("public");
    keywords.addElement("rest");
    keywords.addElement("return");
    keywords.addElement("short");
    keywords.addElement("static");
    keywords.addElement("super");
    keywords.addElement("switch");
    keywords.addElement("synchronized");
    keywords.addElement("this");
    keywords.addElement("throw");
    keywords.addElement("throws");
    keywords.addElement("transient");
    keywords.addElement("true");
    keywords.addElement("try");
    keywords.addElement("var");
    keywords.addElement("void");
    keywords.addElement("volatile");
    keywords.addElement("while");
    doc.setKeywords(keywords);
    editor.setDocument(doc);
    frame.setSize(400,400);
    frame.getContentPane().add(editor);
    frame.show();
  }
}

Listing 3.
import com.sun.java.swing.*;
import com.sun.java.swing.text.*;
import java.util.*;
import java.awt.*;

public class CodeDocument extends DefaultStyledDocument{
  private String word = "";
  private SimpleAttributeSet bold = new SimpleAttributeSet();
  private SimpleAttributeSet string = new SimpleAttributeSet();
  private SimpleAttributeSet normal = new SimpleAttributeSet();
  private SimpleAttributeSet number = new SimpleAttributeSet();
  private SimpleAttributeSet comments = new SimpleAttributeSet();
  private int currentPos = 0;
  private Vector keywords = new Vector();
  public static int STRING_MODE = 10;
  public static int TEXT_MODE = 11;
  public static int NUMBER_MODE = 12;
  public static int COMMENT_MODE = 13;
  private int mode = TEXT_MODE;
 

  public CodeDocument() {
   //set the bold attribute
   StyleConstants.setBold(bold, true);
   StyleConstants.setForeground(string, Color.red);
   StyleConstants.setForeground(number, Color.magenta);
   StyleConstants.setForeground(comments, Color.blue);
   StyleConstants.setItalic(comments, true);
  }
 

  private void insertKeyword(String str, int pos){
    try{
      //remove the old word and formatting
      this.remove(pos - str.length(), str.length());
      /*replace it with the same word, but new formatting
      *we MUST call the super class insertString method here, otherwise we
      *would end up in an infinite loop !!!!!*/
      super.insertString(pos - str.length(), str, bold);
    }
    catch (Exception ex){
      ex.printStackTrace();
    }
  }
 

  private void insertTextString(String str, int pos){
    try{
      //remove the old word and formatting
      this.remove(pos,str.length());
      super.insertString(pos, str, string);
    }
    catch (Exception ex){
      ex.printStackTrace();
    }
  }
 

  private void insertNumberString(String str, int pos){
    try{
      //remove the old word and formatting
      this.remove(pos,str.length());
      super.insertString(pos, str, number);
    }
    catch (Exception ex){
      ex.printStackTrace();
    }
  }
 

  private void insertCommentString(String str, int pos){
    try{
      //remove the old word and formatting
      this.remove(pos,str.length());
      super.insertString(pos, str, comments);
    }
    catch (Exception ex){
      ex.printStackTrace();
    }
  }
 

  private void checkForString(){
    int offs = this.currentPos;
    Element element = this.getParagraphElement(offs);
    String elementText = "";
    try{
      //this gets our chuck of current text for the element we're on
      elementText = this.getText(element.getStartOffset(),
                                 element.getEndOffset() -
element.getStartOffset());
    }
    catch(Exception ex){
      //whoops!
      System.out.println("no text");
    }
    int strLen = elementText.length();
    if (strLen == 0) {return;}
    int i = 0;
 

    if (element.getStartOffset() > 0){
      //translates backward if neccessary
      offs = offs - element.getStartOffset();
    }
    int quoteCount = 0;
    if ((offs >= 0) && (offs <= strLen-1)){
      i = offs;
      while (i >0){
      //the while loop walks back until we hit a delimiter
 

        char charAt = elementText.charAt(i);
        if ((charAt == '"')){
         quoteCount ++;
        }
        i--;
      }
      int rem = quoteCount % 2;
      //System.out.println(rem);
      mode = (rem == 0) ? TEXT_MODE: STRING_MODE;
    }
  }
 

  private void checkForKeyword(){
    if (mode != TEXT_MODE) {
      return;
    }
    int offs = this.currentPos;
    Element element = this.getParagraphElement(offs);
    String elementText = "";
    try{
      //this gets our chuck of current text for the element we're on
      elementText = this.getText(element.getStartOffset(),
element.getEndOffset() - element.getStartOffset());
    }
    catch(Exception ex){
      //whoops!
      System.out.println("no text");
    }
    int strLen = elementText.length();
    if (strLen == 0) {return;}
    int i = 0;
 

    if (element.getStartOffset() > 0){
      //translates backward if neccessary
      offs = offs - element.getStartOffset();
    }
    if ((offs >= 0) && (offs <= strLen-1)){
      i = offs;
      while (i >0){
      //the while loop walks back until we hit a delimiter
        i--;
        char charAt = elementText.charAt(i);
        if ((charAt == ' ') | (i == 0) | (charAt =='(') | (charAt ==')') |
            (charAt == '{') | (charAt == '}')){ //if i == 0 then we're at
the begininng
          if(i != 0){
            i++;
          }
          word = elementText.substring(i, offs);//skip the period
 

          String s = word.trim().toLowerCase();
          //this is what actually checks for a matching keyword
          if (keywords.contains(s)){
            insertKeyword(word, currentPos);
          }
          break;
        }
      }
    }
  }
 

  private void checkForNumber(){
    int offs = this.currentPos;
    Element element = this.getParagraphElement(offs);
    String elementText = "";
    try{
      //this gets our chuck of current text for the element we're on
      elementText = this.getText(element.getStartOffset(),
element.getEndOffset() - element.getStartOffset());
    }
    catch(Exception ex){
      //whoops!
      System.out.println("no text");
    }
    int strLen = elementText.length();
    if (strLen == 0) {return;}
    int i = 0;
 

    if (element.getStartOffset() > 0){
      //translates backward if neccessary
      offs = offs - element.getStartOffset();
    }
    mode = TEXT_MODE;
    if ((offs >= 0) && (offs <= strLen-1)){
      i = offs;
      while (i >0){
      //the while loop walks back until we hit a delimiter
        char charAt = elementText.charAt(i);
        if ((charAt == ' ') | (i == 0) | (charAt =='(') | (charAt ==')') |
            (charAt == '{') | (charAt == '}') /*|*/){ //if i == 0 then
we're at the begininng
          if(i != 0){
            i++;
          }
          mode = NUMBER_MODE;
          break;
        }
        else if (!(charAt >= '0' & charAt <= '9' | charAt=='.'
                  | charAt=='+' | charAt=='-'
                  | charAt=='/' | charAt=='*'| charAt=='%' | charAt=='=')){
          mode = TEXT_MODE;
          break;
        }
        i--;
      }
    }
  }
 

  private void checkForComment(){
    int offs = this.currentPos;
    Element element = this.getParagraphElement(offs);
    String elementText = "";
    try{
      //this gets our chuck of current text for the element we're on
      elementText = this.getText(element.getStartOffset(),
element.getEndOffset() - element.getStartOffset());
    }
    catch(Exception ex){
      //whoops!
      System.out.println("no text");
    }
    int strLen = elementText.length();
    if (strLen == 0) {return;}
    int i = 0;
 

    if (element.getStartOffset() > 0){
      //translates backward if neccessary
      offs = offs - element.getStartOffset();
    }
    if ((offs >= 1) && (offs <= strLen-1)){
      i = offs;
      char commentStartChar1 = elementText.charAt(i-1);
      char commentStartChar2 = elementText.charAt(i);
      if (commentStartChar1 == '/' && commentStartChar2 == '*'){
          mode = COMMENT_MODE;
          this.insertCommentString("/*", currentPos-1);
      }
      else if (commentStartChar1 == '*' && commentStartChar2 == '/'){
          mode = TEXT_MODE;
          this.insertCommentString("*/", currentPos-1);
      }
    }
  }
 

  private void processChar(String str){
    char strChar = str.charAt(0);
    if (mode != this.COMMENT_MODE){
      mode = TEXT_MODE;
    }
      switch (strChar){
        case ('{'):case ('}'):case (' '): case('\n'):
        case ('('):case (')'):case (';'):case ('.'):{
          checkForKeyword();
          if (mode == STRING_MODE && strChar == '\n'){
            mode = TEXT_MODE;
          }
        }
        break;
        case ('"'):{
          insertTextString(str, currentPos);
          this.checkForString();
        }
        break;
        case ('0'):case ('1'):case ('2'):case ('3'):case ('4'):
        case ('5'):case ('6'):case ('7'):case ('8'):case ('9'):{
          checkForNumber();
        }
        break;
        case ('*'):case ('/'):{
          checkForComment();
        }
        break;
      }
      if (mode == this.TEXT_MODE){
        this.checkForString();
      }
      if (mode == this.STRING_MODE){
        insertTextString(str, this.currentPos);
      }
      else if (mode == this.NUMBER_MODE){
        insertNumberString(str, this.currentPos);
      }
      else if (mode == this.COMMENT_MODE){
        insertCommentString(str, this.currentPos);
      }
 

  }
 

  private void processChar(char strChar){
      char[] chrstr = new char[1];
      chrstr[0] = strChar;
      String str = new String(chrstr);
      processChar(str);
  }
 

  public void insertString(int offs,
                          String str,
                          AttributeSet a) throws BadLocationException{
    super.insertString(offs, str, normal);
 

    int strLen = str.length();
    int endpos = offs + strLen;
    int strpos;
    for (int i=offs;i<endpos;i++){
      currentPos = i;
      strpos = i - offs;
      processChar(str.charAt(strpos));
    }
    currentPos = offs;
  }
 

  public Vector getKeywords(){
    return this.keywords;
  }
 

  public void setKeywords(Vector aKeywordList){
    if (aKeywordList != null){
      this.keywords = aKeywordList;
    }
  }
}