Question

我正在尝试设计一个可以应用于声明类型的子类的arg函数：

但是当我将这样的函数应用于类型T时，如下所示：

Function<? extends T,Boolean> function;
function.apply(T)

我收到以下编译错误：

T cannot be converted to capture#2 of ? extends T

我试图设计的验证界面示例：

//Intent is that the function can be applied to T, or any subclass of T
public interface IBeanValidator<T> {
    public Function<? extends T, Boolean> getValidation();
}

//Class that implements this interface will accept validators for its type
public interface IValidateableBean<T> {
    public void validate(final IBeanValidator<T> validator);
}

//Interface for bean objects, which can be validated with validators designed
//for beans belong to this inheritane hierarchy
public interface IBean extends IValidateableBean<IBean> {
    public default void validate(final IBeanValidator<IBean> validator) {
        //compilation error occurs here. 
        validator.getValidation().apply(this);
    }
}

Answer 1

而不是Function<? extends T, Boolean>，您实际上只需要一个Function<T, Boolean>，其中将接受T的子类型。Function<? extends T, Boolean>实际上是指一些未知但具体的T的子类型，例如Function<SubT, Boolean>，不一定适用于任何T。

如何定义一个灵活接受声明类型的子类的Function

1 个答案: