Generic super class in java

Question

Is it possible to create something like this in java

public abstract class GenericView<LAYOUTTYPE extends AbstractLayout> extends LAYOUTTYPE

so that

public class MyView extends GenericView<HorizontalLayout>

extends GenericView and HorizontalLayout and

public class MyView2 extends GenericView<VerticalLayout>

extends GenericView and VerticalLayout?

Answer 1

The short answer - no. The type you extends must be an actual type, not a generic type parameter.

Answer 2

It sounds like you want to accomplish multiple inheritance, inheriting from both a View and a Layout. This is not possible in Java. You can accomplish something similar with composition. If your GenericView must also provide the functionality given by AbstractLayout, then you can accomplish it like this:

public interface Layout {
    // Layout functions
    public void doLayout();
}

public class GenericView<T extends AbstractLayout> implements Layout {
    private final T delegateLayout;

    // Construct with a Layout
    public GenericView(T delegateLayout) {
        this.delegateLayout = delegateLayout;
    }

    // Delegate Layout functions (Eclipse/IntelliJ can generate these for you):
    public void doLayout() {
        this.delegateLayout.doLayout();
    }

    // Other GenericView methods
}

public class VerticalLayout extends AbstractLayout {
    public void doLayout() {
        // ...
    }
}

After this, you can actually do this:

new GenericView<VerticalLayout> (new VerticalLayout());

Hope this helps.