How to convert sync method to async method in Java 1.4

Question

I need to convert a sync method like next:

method (String, String, Object)

to an async method.

The main problem is that we work with Java 1.4 and I can't use Executor, Future, ...

Any ideas?

Answer 1

Define a callback interface (if one isn't already available) and make your method take the interface as a parameter. The method will go off and do its work, and when it's finished, it calls the callback.

Example:

int synchronousMethod(int arg0, String arg1) {
    int result = doStuff();
    return result;
}

becomes

void asynchronousMethod(int arg0, String arg1, Callback callback) {
    try {
        int result = doStuff();
    } catch (Throwable t) {
        callback.onFailure(t);
        return;
    }
    callback.onSuccess(result);
}

where Callback is something like

interface Callback {
    onSuccess(int result);
    onFailure(Throwable t);
}

It's preferable to use generic types for the Callback result (GWT, for example, uses a generic AsyncCallback<ResultType> that is identical to the interface above), but since generics aren't available in 1.4, you can either use Object and cast or have different Callback interfaces for different returns. Compare with any of the *Listener interfaces in Swing/AWT.