所有已实现类中的启动方法

Question

I'm kind of new to Java and have a rather simple question:

I have an interface, with a method:

public interface Interface_Updatable {

    public void updateViewModel();

}

I implement this interface in several classes. Each class then of course has that method updateViewModel .

Edit: I instantiate these classes in a main function. Here I need code that calls updateViewModel for all objects that implement the interface.

Is there an easy way to do it combined? I don't want to call every method from every object instance separately and keep that updated. Keeping it updated might lead to errors in the long run.

Answer 1

The short form is: no , there's no simple way to "call this method on all instances of classes that implement this interface".

At least not in a way that's sane and maintainable.

So what should you do instead?

In reality you almost never want to just "call it on all instances", but you have some kind of relation between the thing that should trigger the update and the instances for which it should be triggered.

For example, the naming of the method suggests that instances of Interface_Updatable are related to the view model. So if they "care" about changes to the view model, they could register themselves as interested parties by doing something like theViewModel.registerForUpdates(this) , the view model could hold on to a list of all objects that registered like this and then loop over all the instances and calls updateViewModel on each one (of course one would need to make sure that unregistration also happens, where appropriate).

This is the classical listener pattern at work.

But the high-level answer is: you almost never want to call something on "all instances", instead the instances you want to call it on have some relation to each other and you would need to make that relation explicit (via some registration mechanism like the one described above).

Answer 2

There is no easy way to call this method on all classes that implement this interface. The problem is that you need to somehow keep track of all the classes that implement this interface.

A possible object-oriented way to do this would be passing a list containing objects that are instances of classes that implement the Interface_Updateable interface to a function, and then calling updateViewModel on each object in that list:

public void updateViewModels(List<Interface_Updateable> instances) {
    for(var instance : instances) {
        instance.updateViewModel();
    }
}