How should I replicate the functionality of C#'s 'using' keyword in Java?

Question

I'm converting some C# code to Java and it contains the using keyword. How should I replicate this functionality in Java? I was going to use a try, catch, finally block but I thought I'd check with you guys first.

Answer 1

That's correct. A C# using block is just syntactic sugar for that anyway. The closest Java equivalent to IDisposable is Closeable.

There is a proposal (which is partially committed already), called Automatic Resource Management, for adding similar functionality to Java 7. It would use try-finally behind the scenes, and proposes creating a new Disposable interface (which would be a superinterface of Closeable).

Answer 2

Don't forget the null checking! That is to say

using(Reader r = new FileReader("c:\test")){ //some code here }

should be translated to something like

Reader r = null; try{ //some code here } finally{ if(r != null){ r.close() } }

And also most close() in java throw exceptions, so check DbUtils.closeQuietly if you want your code to be more c# like

Answer 3

The standard idiom for resource handling in Java is:

final Resource resource = acquire();
try {
    use(resource);
} finally {
    resource.dispose();
}

Common mistakes include trying to share the same try statement with exception catching and following on from that making a mess with nulls and such.

The Execute Around Idiom can extract constructs like this, although the Java syntax is verbose.

executeWith(new Handler() { public void use(Resource resource) {
    ...
}});