Saturday, February 28, 2009

Small Language Changes for JDK7

For those who haven't been paying attention, there is a new project from Sun to attract proposals for small language changes to JDK7. Even in the first day of open calls for proposals, the entries have been very interesting:
  • Strings in Switch, a proposal from Joe Darcy to be able to use Strings in switch statements.

  • Automated Resource Blocks, a proposal from Josh Bloch to be able to say things like:

    try (BufferedReader br = new BufferedReader(new FileReader(path)) {
    return br.readLine();
    instead of:

    BufferedReader br = new BufferedReader(new FileReader(path));
    try {
    return br.readLine();
    } finally {
    based on having BufferedReader implement a Disposable interface.

  • Block expressions, a proposal from Neal Gafter to be allow things like:
    double pi2 = (double pi = Math.PI ; pi*pi)**; // pi squared*

    Basically, the principle here is that the (parenthesis-delimited) block would return a value.

  • Exception handling improvements, another proposal from Neal Gafter to allow things like:
    try {
    } catch (final IOException | SQLException ex) {
    throw ex;

  • Improved Type Inference, a proposal from me (although I can't claim credit for the idea) to be able to replace things like this:
    Map<String, List<String>> anagrams = new HashMap<String, List<String>>();
    with things like this:
    Map<String, List<String>> anagrams = new HashMap<>();

  • A new syntax for wildcard variance, again from the prolific Neal Gafter, allowing the user to replace "? extends" with "out" and "? super" with "in". (Can you tell that Neal's been working on C#?)

I don't love all of these proposals, but I do love some of them, and I think it is great to see that the pent-up demand for work on the Java language finally has an outlet.

(For those of you following the various Closures proposals: Closures don't count as a small change, and are therefore not in scope for this JSR.)

ETA: The "use Scala instead" and "where is BGGA?" comments have been made, so please read the comments and feedback before reiterating them.