question: public final int indexOf ( java . lang . CharSequence csq , int fromIndex ) { if ( ( _offset + fromIndex + csq . length ( ) - 1 ) >= ( _offset + _length ) ) throw new IndexOutOfBoundsException ( String . format ( "From Index %d Is Out of Bounds" , fromIndex ) ) ; final char c = csq . charAt ( 0 ) ; final int csqLength = csq . length ( ) ; for ( int i = _offset + fromIndex , end = _offset + _length - csqLength + 1 ; i < end ; i ++ ) { if ( _array [ i ] == c ) { boolean match = true ; for ( int j = 1 ; j < csqLength ; j ++ ) { if ( _array [ i + j ] != csq . charAt ( j ) ) { match = false ; break ; } } if ( match ) { return i - _offset ; } } } return - 1 ; }
target:  Returns the index within this character sequence of the first occurrence of the specified characters sequence searching forward, starting from the specified index