public synchronized StringBuffer insert(int offset, char ch)
public synchronized StringBuffer insert(int offset, char[] str, int str_offset, int len)
  public synchronized StringBuffer insert(int offset, char ch)  {    if (offset < 0 || offset > count)      throw new StringIndexOutOfBoundsException(offset);    ensureCapacity_unsynchronized(count + 1);    System.arraycopy(value, offset, value, offset + 1, count - offset);    value[offset] = ch;    count++;    return this;  }