public synchronized StringBuffer insert(int offset, String str)
public synchronized StringBuffer insert(int offset, char[] str, int str_offset, int len)
  public synchronized StringBuffer insert(int offset, String str)  {    if (offset < 0 || offset > count)      throw new StringIndexOutOfBoundsException(offset);    if (str == null)      str = "null";    int len = str.count;    ensureCapacity_unsynchronized(count + len);    System.arraycopy(value, offset, value, offset + len, count - offset);    str.getChars(0, len, value, offset);    count += len;    return this;  }