UnionToken(int type) 
{
          
            super(type);
}

  void addChild(Token tok) 
{
            if (tok == null)  return;
            if (this.children == null)  this.children = new Vector();
            if (this.type == UNION) {
                this.children.addElement(tok);
                return;
            }
                                                // This is CONCAT, and new child is CONCAT.
            if (tok.type == CONCAT) {
                for (int i = 0;  i <  tok.size();  i ++)
                    this.addChild(tok.getChild(i)); // Recursion
                return;
            }
            int size = this.children.size();
            if (size == 0) {
                this.children.addElement(tok);
                return;
            }
            Token previous = (Token)this.children.elementAt(size-1);
            if (!((previous.type == CHAR || previous.type == STRING)
                  && (tok.type == CHAR || tok.type == STRING))) {
                this.children.addElement(tok);
                return;
            }
            //System.err.println("Merge '"+previous+"' and '"+tok+"'.");
            StringBuffer buffer;
            int nextMaxLength = (tok.type == CHAR ? 2 : tok.getString().length());
            if (previous.type == CHAR) {        // Replace previous token by STRING
                buffer = new StringBuffer(2 + nextMaxLength);
                int ch = previous.getChar();
                if (ch  >= 0x10000)
                    buffer.append(REUtil.decomposeToSurrogates(ch));
                else
                    buffer.append((char)ch);
                previous = Token.createString(null);
                this.children.setElementAt(previous, size-1);
            } else {                            // STRING
                buffer = new StringBuffer(previous.getString().length() + nextMaxLength);
                buffer.append(previous.getString());
            }
            if (tok.type == CHAR) {
                int ch = tok.getChar();
                if (ch  >= 0x10000)
                    buffer.append(REUtil.decomposeToSurrogates(ch));
                else
                    buffer.append((char)ch);
            } else {
                buffer.append(tok.getString());
            }
            ((StringToken)previous).string = new String(buffer);
}

 Token getChild(int index) 
{
            return (Token)this.children.elementAt(index);
}

 int size() 
{
            return this.children == null ? 0 : this.children.size();
}

 public String toString(int options) 
{
            String ret;
            if (this.type == CONCAT) {
                if (this.children.size() == 2) {
                    Token ch = this.getChild(0);
                    Token ch2 = this.getChild(1);
                    if (ch2.type == CLOSURE && ch2.getChild(0) == ch) {
                        ret = ch.toString(options)+"+";
                    } else if (ch2.type == NONGREEDYCLOSURE && ch2.getChild(0) == ch) {
                        ret = ch.toString(options)+"+?";
                    } else
                        ret = ch.toString(options)+ch2.toString(options);
                } else {
                    StringBuffer sb = new StringBuffer();
                    for (int i = 0;  i <  this.children.size();  i ++) {
                        sb.append(((Token)this.children.elementAt(i)).toString(options));
                    }
                    ret = new String(sb);
                }
                return ret;
            }
            if (this.children.size() == 2 && this.getChild(1).type == EMPTY) {
                ret = this.getChild(0).toString(options)+"?";
            } else if (this.children.size() == 2
                       && this.getChild(0).type == EMPTY) {
                ret = this.getChild(1).toString(options)+"??";
            } else {
                StringBuffer sb = new StringBuffer();
                sb.append(((Token)this.children.elementAt(0)).toString(options));
                for (int i = 1;  i <  this.children.size();  i ++) {
                    sb.append((char)'|");
                    sb.append(((Token)this.children.elementAt(i)).toString(options));
                }
                ret = new String(sb);
            }
            return ret;
}