Hello Java World ~> Parsing a Sudoku Grid

This is my first, very-very first attempt at java. I haven't started tackling the actual resolution of the sudoku puzzle (not even sure where to start, haven't looked at other weekend-challenge entries yet). I don't have much to go over here, but I'm sure it's filled with beginner mistakes already, so before I make things any worse I'd like to get a review of what I have.

The puzzle being parsed is the one provided as an example in the winning weekend-challenge suggestion.

public class SudokuGame {

    private final static String newLine = System.lineSeparator();
    private final static String puzzle = 
            "...84...9" + newLine +
            "..1.....5" + newLine +
            "8...2146." + newLine +
            "7.8....9." + newLine +
            "........." + newLine +
            ".5....3.1" + newLine +
            ".2491...7" + newLine +
            "9.....5.." + newLine +
            "3...84...";

    public static void main(String[] args){
        SudokuGrid grid = new SudokuGrid(puzzle);
        System.out.print(grid);
    }
}

The program takes the string and outputs this:

+===========+===========+===========+
|   |   |   | 8 | 4 |   |   |   | 9 |
-------------------------------------
|   |   | 1 |   |   |   |   |   | 5 |
-------------------------------------
| 8 |   |   |   | 2 | 1 | 4 | 6 |   |
+===========+===========+===========+
| 7 |   | 8 |   |   |   |   | 9 |   |
-------------------------------------
|   |   |   |   |   |   |   |   |   |
-------------------------------------
|   | 5 |   |   |   |   | 3 |   | 1 |
+===========+===========+===========+
|   | 2 | 4 | 9 | 1 |   |   |   | 7 |
-------------------------------------
| 9 |   |   |   |   |   | 5 |   |   |
-------------------------------------
| 3 |   |   |   | 8 | 4 |   |   |   |
+===========+===========+===========+

Here's the SudokuGrid class:

```
/** A 9x9 Sudoku grid */
public class SudokuGrid {

private SudokuDigit[][] digits;

/** Creates a new Su

-
Instead of your String puzzle you could use an String[] like below (not saying you have to, but you should know that the alternative exists). You are currently converting it to a String array later anyway, so why not have it as a String array right from the start?

private final static String[] puzzle = new String[]{ "...84...9", "..1.....5", ... };

-
This can be marked with final: private SudokuDigit[][] digits; to prevent any malicious programmer from even trying to use this.digits = null after it has once been initialized, or initialize a new 2-dimensional array

-
3 is a magic number. Yes it is, it's a magic number. In the past in the present and the future, I say three, is a magic number.

-
9 is also magic number. This means that you should use it as a constant:

public static final int MAGIC_NUMBER = 9;

-
A double for-loop with variables i and j can be called x and y instead, to avoid any possible confusion about which one is which.

-
UnsupportedOperationException might not be the best exception to throw in your setDigit method. IllegalArgumentException would be better, since the argument to the method is incorrect.

-
Simplification possible in your SudokuDigit char constructor:

numericValue = value == '.' ? null : Integer.parseInt(String.valueOf(value));

-
When writing JavaDoc, I believe it's convention to use it on multiple lines. Or at least that's more common than using only one line (Also, did you know that you could write /** before a method in Eclipse and then press enter to make Eclipse write the basic "layout" of it for you?)

/**
 * Creates a new digit from specified character.
 */
public SudokuDigit(char value) {

-
You can use @throws in Javadoc to specify What exception can be thrown, and why.

/** 
 * Sets the current value of the digit.
 * Specify null for no value. 
 * @throws UnsupportedOperationException if value is not valid.
 */ 
public void setDigit(Integer value) {

-
You can use Character.digit(char c, int radix) instead of Integer.parseInt to convert your chars to int. Such as Character.digit(value, 10)

If I wouldn't have known it, I wouldn't be able to tell that you are a Java beginner. You seem to be following nearly all of the common conventions and seem to be doing things well overall. Not much to complain about, really.

StackExchange Code Review Q#37435, answer score: 4