question: public String convertB ( int num ) { int mask = 15 ; StringBuffer sb = new StringBuffer ( ) ; while ( num != 0 ) { int index = ( num & mask ) ; char c = ( char ) ( ( index < 10 ) ? ( index + '0' ) : ( 'a' + index - 10 ) ) ; sb . append ( c ) ; num = num > > > 4 ; } sb . reverse ( ) ; return sb . toString ( ) ; }
target:  Using bit mask and bit-wise operation