question: public StrBuilder replaceFirst ( final String searchStr , final String replaceStr ) { final int searchLen = ( searchStr == null ? 0 : searchStr . length ( ) ) ; if ( searchLen > 0 ) { final int index = indexOf ( searchStr , 0 ) ; if ( index >= 0 ) { final int replaceLen = ( replaceStr == null ? 0 : replaceStr . length ( ) ) ; replaceImpl ( index , index + searchLen , searchLen , replaceStr , replaceLen ) ; } } return this ; }
target:  Replaces the first instance of the search string with the replace string.