Closures are a popular programming tool in many languages. While Java does not yet provide closures, a group of experts, led by Neal Gafter, are working on a proposal to add closures to Java. The proposed specification can be found at JSR Proposal: Closures for Java.

The latest closures proposal update includes support for the use-case of employing closures as control structures. In a recent blog post, Closures: Control Abstraction, Method References, Puzzler Solution, Neal Gafter illustrates this use of closures:

[When] you're writing a method intended to be used as a control API, you can write a function type with the (new) ==> token to designate an unrestricted function (interface) type. Let's do that to write a method, with, that will automatically close a stream for us.

The idea is to be able to replace this code...

FileInputStream input = new FileInputStream(fileName);
try {
    // use input
} finally {
    try {
        input.close();
    } catch (IOException ex) {
        logger.log(Level.SEVERE, ex.getMessage(), ex);
    }
}

with this:

with (FileInputStream input : new FileInputStream(fileName)) {
    // use input
}

which is an invocation of the following method:

public static void with(FileInputStream t, {FileInputStream==>void} block) {
    try {
        block.invoke(t);
    } finally {
        try {
            t.close();
        } catch (IOException ex) {
            logger.log(Level.SEVERE, ex.getMessage(), ex);
        }
    }
}

This is among the simplest control APIs...

What do you think of the latest additions to the Closures for Java proposal?