PrintGrid.java

import java.util.InputMismatchException;
import java.util.Scanner;


public class PrintGrid
{
    public static void main( String[] args ) {
        Scanner scan = new Scanner( System.in );
        int rows = readInt(
            "How many rows (positive integer)?", scan
        );
        int cols = readInt(
            "How many columns (positive integer)?", scan
        );

        print( rows, cols );
    }

    private static void print( int rows, int cols ) {
        // display width to which each number should be padded
        int maxWidth = 2 + ("" + rows*cols).length();
        // THIS IS THE PART YOU WANT...REST IS PROOF-OF-CONCEPT
        for (int i = 1; i <= rows; i++) {
            for (int j = 0; j < cols; j++) {
                // i + j*rows with i running from 1 to rows and
                // j running from 0 to cols - 1 is the answer
                System.out.print( pad( maxWidth, i + j*rows ));
            }
            System.out.println();   // start next row
        }
        //////////////////////////////////////////////////////
    }

    private static String pad( int maxWidth, int num ) {
        //pad num on left with blanks to width of maxWidth
        String maxPad = "          ";
        int idx = maxPad.length() - maxWidth + ("" + num).length();
        return maxPad.substring( idx ) + num;
    }
    private static int readInt( String prompt, Scanner scan ) {
        int i = 0;  // set return into method-global scope
        // read until valid input given
        while (true) {
            System.out.println( prompt );
            try {
                i = scan.nextInt();
                break;
            }
            catch( InputMismatchException e ) {
                String sink = scan.next();
                System.out.println(
                    "invalid value: " + sink + "\n" +
                    e.toString()
                );
            }
        }
        return i;
    }
}