子类化（通用）构建器的子类

Question

我正在尝试使用多级 inheritance 实现构建器 object。 我从Subclassing a Java Builder class中获得了一些灵感，这是我的（简化的）代码：

public class StackOverflow {
    public static class Builder<T extends Builder<T>> {
        public Builder() {}

        public T doA() {
            System.out.println("A");
            return (T) this;
        }
    }

    public static class BuilderSubclass <T extends BuilderSubclass<T>> 
            extends Builder<BuilderSubclass<T>> {

        public BuilderSubclass() {}

        public T doB() {
            System.out.println("B");
            return (T) this;
        }
    }

    public static class BuilderSubclassSubclass
            extends BuilderSubclass<BuilderSubclassSubclass> {

        public BuilderSubclassSubclass() {}

        public BuilderSubclassSubclass doC() {
            System.out.println("C");
            return this;
        }
    }
}

我想做这样的事情： new StackOverflow.BuilderSubclassSubclass().doA().doC().doB()

但是，当我调用new StackOverflow.BuilderSubclassSubclass().doA()时，返回的 object 不是BuilderSubclassSubclass而是BuilderSubclass<BuilderSubclassSubclass> 。 我知道为什么会这样： Builder的泛型类型是BuilderSubclass<BuilderSubclassSubclass> ，它在 BuilderSubclass 的BuilderSubclass签名中分配。

关于如何避免这个问题的任何想法？

更新：我想我可以避免使用构建器模式，而是像这样调用函数：

StackOverflow.BuilderSubclassSubclass builder = new StackOverflow.BuilderSubclassSubclass();
builder.doA();
builder.doB();
builder.doC();

在这种情况下，代码变为：

public class StackOverflowBatchHelperFunctions {
    public static class Builder {

        public Builder() {
        }

        public void doA() {
            System.out.println("A");
        }
    }

    public static class BuilderSubclass extends Builder {
        public BuilderSubclass() {
            super();
        }

        public void doB() {
            System.out.println("B");
        }
    }

    public static class BuilderSubclassSubclass extends BuilderSubclass {
        public BuilderSubclassSubclass() {
            super();
        }

        public void doC() {
            System.out.println("C");
        }
    }
}

但是我认为这不那么“漂亮”，所以我仍然希望看到最初问题的答案。

Answer 1

You should replace public static class BuilderSubclass<T extends BuilderSubclass<T>> extends Builder<BuilderSubclass<T>> with public static class BuilderSubclass<T extends BuilderSubclass<T>> extends Builder<T> .