子类化（通用）构建器的子类

Question

我正在尝试实现具有多级继承的构建器对象。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 Whosebug {
    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 Whosebug.BuilderSubclassSubclass().doA().doC().doB()

但是，当我调用 new Whosebug.BuilderSubclassSubclass().doA() 时，返回的对象不是 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 class 签名中分配。

关于如何避免这个问题有什么想法吗？

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：

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

在这种情况下，代码变为：

public class WhosebugBatchHelperFunctions {
    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");
        }
    }
}

不过我认为这还不够"pretty"，所以我仍然希望看到最初问题的答案。

Answer 1

您应该将 public static class BuilderSubclass<T extends BuilderSubclass<T>> extends Builder<BuilderSubclass<T>> 替换为 public static class BuilderSubclass<T extends BuilderSubclass<T>> extends Builder<T>。

子类化（通用）构建器的子类

Subclassing a subclass of a (generic) builder

java

generics

builder