code: public void append(char c) {
          if (this.length + 1 > this.ch.length) {
                      int newLength = this.ch.length*2;
                      if (newLength < this.ch.length + DEFAULT_SIZE)
                          newLength = this.ch.length + DEFAULT_SIZE;
                      char[] newch = new char[newLength];
                      System.arraycopy(this.ch, 0, newch, 0, this.length);
                      this.ch = newch;
          }
          this.ch[this.length] = c;
          this.length++;
      }
docs: append
  
  @param c