question: public static String toString ( int M_ [ ] [ ] ) { StringBuilder sb = new StringBuilder ( ) ; for ( int j = 0 ; j < M_ . length ; j ++ ) { for ( int k = 0 ; k < M_ [ j ] . length ; k ++ ) { String num = String . format ( "%5d" , M_ [ j ] [ k ] ) ; sb . append ( num ) ; } sb . append ( "\n" ) ; } return sb . toString ( ) ; }
target:  ToString - return a String representation.