Java通用生成器 [英] Java generic builder

问题描述

假设我需要一些 DerivedBuilder 来扩展一些 BaseBuilder 。基本生成器具有类似 foo 的方法（该方法返回 BaseBuilder ）。派生的构建器具有方法 bar 。方法 bar 应该在方法 foo 之后调用。为此，我可以在 DerivedBuilder 中重写 foo 方法，如下所示：

Suppose I need some DerivedBuilder to extend some BaseBuilder. Base builder has some method like foo (which returns BaseBuilder). Derived builder has method bar. Method bar should be invoked after method foo. In order to do it I can override foo method in DerivedBuilder like this:

@Override
public DerivedBuilder foo() {
    super.foo();
    return this;
}

问题是 BaseBuilder 有很多方法，如 foo ，我必须重写它们中的每一个。我不想这样做，所以我尝试使用泛型：

The problem is that BaseBuilder has a lot of methods like foo and I have to override each one of them. I don't want to do that so I tried to use generics:

public class BaseBuilder<T extends BaseBuilder> {
    ...

    public T foo() {
        ...
        return (T)this;
    }
}

public class DerivedBuilder<T extends DerivedBuilder> extends BaseBuilder<T> {
    public T bar() {
        ...
        return (T)this;
    }
}

但是问题是我仍然不能写

But the problem is that I still can not write

new DerivedBuilder<DerivedBuilder>()
        .foo()
        .bar()

即使 T 此处为 DerivedBuilder 。我该怎么做才能不覆盖很多功能？

Even though T here is DerivedBuilder. What can I do in order to not to override a lot of functions?

推荐答案

您的问题是<$ c $的定义c> DerivedBuilder ：

class DerivedBuilder<T extends DerivedBuilder>;

然后使用类型为擦除参数 new DerivedBuilder< DerivedBuilder<的实例化它。 ..what？...>>（）。

And then instantiating it with a type erased argument new DerivedBuilder<DerivedBuilder<...what?...>>().

您需要一个完全定义的派生类型，例如： / p>

You'll need a fully defined derived type, like this:

public class BaseBuilder<T extends BaseBuilder<T>> {
    @SuppressWarnings("unchecked")
    public T foo() {
        return (T)this;
    }
}

public class DerivedBuilder extends BaseBuilder<DerivedBuilder> {
    public DerivedBuilder bar() {
        return this;
    }
}

检查 ideone.com 。

这篇关于Java通用生成器的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！