如何使用Java中子类的Class实例对象将对象强制转换为自身的子类？

Question

Let's say I have an abstract class AbstractFragment that has a superclass Fragment :

public abstract class AbstractFragment extends Fragment {
      public abstract updateData();



    public static <FragmentClass extends AbstractFragment>
    ChartClass newInstance(int condition, Class<ChartClass> chartFragmentClass) {

                Constructor<ChartClass> c = chartFragmentClass.getConstructor();

                ChartClass fragment = c.newInstance();

                Bundle args = new Bundle();

                args.putInt("key", condition);
                fragment.setArguments(args);

                return fragment;
    }

And two children of the AbstractFragment class:

public class FirstChildFragment extends AbstractFragment {
          public updateData() {}
}

public class SecondChildFragment extends AbstractFragment {
              public updateData() {}
    }

At runtime, depending on a condition, I want to cast a Fragment object to one of either the first or second children depending on a condition or create a new instance of the child using the static method in the abstract class (I already have this static method figured out), like so:

void onDataLoaded(int condition) {

        Fragment fragment = getChildFragmentManager()
                .findFragmentById(R.id.fragment_container_dashboard_chart);

        Class ChildFragmentClass;
        if (condition == 0) ChildFragmentClass = FirstChildFragment.class;
        else if (condition == 1) ChildFragmentClass = SecondChildFragment.class;
        else throw new RuntimeException("Condition is invalid");

        if (fragment.getClass().isInstance(ChildFragmentClass))
            ((ChildFragmentClass) fragment).updateData();
        else {
            ChildFragmentClass childFragment = ChildFragmentClass.newInstance(5, ChildFragmentClass);
        }
    }

The problem in the above code is that I don't know how to properly cast the fragment object so that it is recognized as an instance of the ChildFragmentClass class. Subsequently, that means my code that attempts to call newInstance is also correct How do I appropriately cast fragment to the ChildFragmentClass and be able to call the appropriate methods? I want the new instance to be an instance of either the first or second child.

Answer 1

ChildFragmentClass is not a class it is a local variable. You should create a new variable and assign it.

This may help with your issues.

if (fragment.getClass().isInstance(AbstractFragment))
    ((AbstractFragment) fragment).updateData();
else {
    Fragment childFragment = AbstractFragment.newInstance(5, ChildFragmentClass);
}