In java, return value within synchronized block seems like bad style. Does it really matter?

It’s absolutely fine – as is returning from a loop, or from a try block which has an appropriate finally block. You just need to be aware of the semantics, at which point it makes perfect sense.

It’s certainly simpler code than introducing a local variable for the sake of it:

// Ick - method body is now more complicated, with no benefit
public boolean addComponent2(Component e) {
    boolean ret;
    synchronized (_components) {
        ret = _components.add(new WeakReference<Component>(e));
    }
    return ret;
}