question: private void replaceImpl ( final int startIndex , final int endIndex , final int removeLen , final String insertStr , final int insertLen ) { final int newSize = size - removeLen + insertLen ; if ( insertLen != removeLen ) { ensureCapacity ( newSize ) ; System . arraycopy ( buffer , endIndex , buffer , startIndex + insertLen , size - endIndex ) ; size = newSize ; } if ( insertLen > 0 ) { insertStr . getChars ( 0 , insertLen , buffer , startIndex ) ; } }
target:  Internal method to delete a range without validation.