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Re: How to initialise a final static String array

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On 3/18/2012 8:55 AM, Cecil Westerhof wrote:
> I want to use final for my static variables. I now do for example:
> 	private static final Connection conn;
> 	private static final Combo      container;
>
> and
> 	static {
> 		Connection tempConn;
> 		Statement  tempStmt;
> 		try {
> 			Class.forName("org.h2.Driver");
> 			tempConn = DriverManager.getConnection(
> 					"jdbc:h2:tcp://localhost/~/databases/stock", "sa", "");
> 			tempStmt = tempConn.createStatement();
> 		} catch (Exception e) {
> 			tempConn = null;
> 			tempStmt = null;
> 		}
> 		conn = tempConn;
> 		stmt = tempStmt;
>
> and
> 		if (conn == null) {
> 			throw new Exception("Could not initialise");
> 		}
>
> The only problem I have is with my array of String.
> I now have:
> 	private static final String[] titles = {
> 		"Stock",
> 		"Number",
> 		"Dare",
> 		"Container"
> 	};
>
> Because when I put it in the static block I get an error.

     Works fine for me. What error do you get?

> Beside this I can execute a statement like:
> 		titles[0] = "changed";

     Yes.  The identifier `titles' is final, and will always refer
to the same String[] array: You cannot set it to null or make it
refer to some other String[] array.  But the String[] array itself
is just like any other array: You can change the contents of its
elements any time you like.

> Can I get the initialisation in the static part? And in such a way
> that the elements can not be changed?

     To the first: Yes, certainly.  To the second: No, Java arrays
are always mutable.

     Nonetheless, there are a few things you can do to work around
some of the issues with array mutability.  If you're worrked about
exposing the array to external code that might muck with it, you
could keep the original array `private' (as you've done) and export
a throw-away copy instead:

	public String[] getTitles() {
	    return titles.clone();
	}

Or you could export an immutable List instead of the array:

	public List<String> getTitles() {
	    return Collections.unmodifiableList(
	        Arrays.asList(titles));
	}

If you're worried that you yourself might accidentally damage the
array, you could even use the List internally:

	private static final List<String> titles =
	    Collections.unmodifiableList(
	        Arrays.asList(
	            "Stock", "Number", "Dare", "Container"));

-- 
Eric Sosman
esosman@ieee-dot-org.invalid

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Thread

How to initialise a final static String array Cecil Westerhof <Cecil@decebal.nl> - 2012-03-18 13:55 +0100
  Re: How to initialise a final static String array Jeff Higgins <jeff@invalid.invalid> - 2012-03-18 09:25 -0400
  Re: How to initialise a final static String array Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-03-18 09:24 -0400
  Re: How to initialise a final static String array Arne Vajhøj <arne@vajhoej.dk> - 2012-03-18 12:20 -0400
    Re: How to initialise a final static String array Lew <noone@lewscanon.com> - 2012-03-18 10:31 -0700
      Re: How to initialise a final static String array Arne Vajhøj <arne@vajhoej.dk> - 2012-03-18 19:04 -0400
        Re: How to initialise a final static String array Lew <noone@lewscanon.com> - 2012-03-18 22:16 -0700
          Re: How to initialise a final static String array Arne Vajhøj <arne@vajhoej.dk> - 2012-03-20 20:01 -0400

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