Java循环泛型类型参数问题

Question

我在 java (17) 应用程序中有这些接口和类：

public interface ISurvey<T extends ISurveyDetails<? extends ISurvey<T>>> {
    void setDetails(T details);
}

public interface ISurveyDetails<T extends ISurvey<? extends ISurveyDetails<T>>> {
    void setSurvey(T survey);
}

public class AppleSurvey implements ISurvey<AppleSurveyDetails> {
    @Override
    public void setDetails(AppleSurveyDetails details) {
    }
}

public class AppleSurveyDetails implements ISurveyDetails<AppleSurvey> {
    @Override
    public void setSurvey(AppleSurvey survey) {
    }
}

public class ComplexGenericUser {
    <T extends ISurveyDetails<ISurvey<T>>> void setDetail(ISurvey<T> survey, Supplier<T> detailMaker) {
        var detail = detailMaker.get();
        detail.setSurvey(survey);
        survey.setDetails(detail);
    }

    void useWithApple() {
        var appleSurvey = new AppleSurvey();
        setDetail(appleSurvey, () -> AppleSurveyDetails::new);
    }
}

除了在

setDetail()

类的

useWithApple()

方法中调用

ComplexGenericUser

之外，整个系统都正常。编译器错误指出

no instance of type variable (T) exists so that AppleSurvey conforms to ISurvey<T>

。我该如何解决这个问题？

Answer 1

AppleSurveyDetails

实现

ISurveyDetails<AppleSurvey>

。为了与您的

setDetail

方法兼容，

AppleSurveyDetails

必须实现

ISurveyDetails<ISurvey<AppleSurveyDetails>>

，而不是

ISurveyDetails<AppleSurvey>

。

我认为正确参数化

setDetail

需要两种类型参数，一种用于调查，一种用于详细信息：

<Details extends ISurveyDetails<Survey>, Survey extends ISurvey<Details>>
void setDetail(Survey survey, Supplier<Details> detailMaker) {
    var detail = detailMaker.get();
    detail.setSurvey(survey);
    survey.setDetails(detail);
}

您还需要修复您的

setDetail

电话 - 供应商应该只是

AppleSurveyDetails::new

，而不是

() -> AppleSurveyDetails::new

。

Answer 2

那么你需要更多仿制药:)

这是固定代码：

public interface ISurvey<S extends ISurvey<S, D>, D extends ISurveyDetails<S, D>> {
    void setDetails(D details);
}

public interface ISurveyDetails<S extends ISurvey<S, D>, D extends ISurveyDetails<S, D>> {
    void setSurvey(S survey);
}

public class AppleSurvey implements ISurvey<AppleSurvey, AppleSurveyDetails> {
    @Override
    public void setDetails(AppleSurveyDetails details) {
    }
}

public class AppleSurveyDetails implements ISurveyDetails<AppleSurvey, AppleSurveyDetails> {
    @Override
    public void setSurvey(AppleSurvey survey) {
    }
}

public class ComplexGenericUser {
    <S extends ISurvey< S, D>, D extends ISurveyDetails<S, D>> void setDetail(S survey, Supplier<D> detailMaker) {
        var detail = detailMaker.get();
        detail.setSurvey(survey);
        survey.setDetails(detail);
    }

    void useWithApple() {
        var appleSurvey = new AppleSurvey();
        Supplier<AppleSurveyDetails> tSupplier = AppleSurveyDetails::new;
        setDetail(appleSurvey, tSupplier);
    }
}