子類化（通用）構建器的子類

Question

我正在嘗試使用多級 inheritance 實現構建器 object。 我從Subclassing a Java Builder class中獲得了一些靈感，這是我的（簡化的）代碼：

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;
        }
    }
}

我想做這樣的事情： new StackOverflow.BuilderSubclassSubclass().doA().doC().doB()

但是，當我調用new StackOverflow.BuilderSubclassSubclass().doA()時，返回的 object 不是BuilderSubclassSubclass而是BuilderSubclass<BuilderSubclassSubclass> 。 我知道為什么會這樣： Builder的泛型類型是BuilderSubclass<BuilderSubclassSubclass> ，它在 BuilderSubclass 的BuilderSubclass簽名中分配。

關於如何避免這個問題的任何想法？

更新：我想我可以避免使用構建器模式，而是像這樣調用函數：

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

在這種情況下，代碼變為：

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");
        }
    }
}

但是我認為這不那么“漂亮”，所以我仍然希望看到最初問題的答案。

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> .