将继承的变量强制转换为子类

Question

I have two closely knit cluster of classes. For the sake of explanation, lets call one the view and the other the template . The template tells the view how to look. I have a base view and base template class and a number of paired subclasses of them.

So, like so:

Base Classes

BaseTemplate <-> BaseView

Subclasses

TemplateA <-> ViewA
TemplateB <-> ViewB
TemplateC <-> ViewC
TemplateD <-> ViewD

The view s (Even the base view ) each have a template , of the corresponding type, as a variable. How can I cast, for example, the variable of BaseTemplate , declared in BaseView , to TemplateB , declared in ViewB ? I would like to be able to set variable information in the BaseTemplate , rather than having to set generic information in all the template subclasses.

Answer 1

It sounds like you could use generics to address this issue. For example:

public abstract class BaseView<T extends BaseTemplate> {

    private final T template;

    protected BaseView(T template) {
        this.template = template;
    }

    //common view methods operating using T etc.
}

public final class ViewA extends BaseView<TemplateA> {

    public ViewA() {
        super(new TemplateA()); //or wherever templates come from
    }

    // ViewA specific stuff
}