java - 如何返回参数化类型的类类型

Question

我的第一次尝试是这样的:

@Override
public Class<? extends Set<Measurement>> getType() {
    Set<Measurement> s = new HashSet<Measurement>();
    return s.getClass();
}

但它无法编译:

incompatible types: java.lang.Classjava.util.Set cannot be converted to java.lang.Class*? extends java.util.Set*mydomain.Measurement**

我的第二次尝试:

@Override
public Class<? extends Set<Measurement>> getType() {
    return Set<Measurement>.class;
}

仍然无法编译:

Cannot select from parameterized type

Answer 1

好吧，您可以通过扩展通用类来做到这一点。这将允许编译器保留类型信息。

public class So45012361Application {

    public class Measurement {}

    public class MeasurementsSet extends HashSet<Measurement> {}

    public Class<? extends Set<Measurement>> getType() {
        MeasurementsSet ms = new MeasurementsSet();
        return ms.getClass();
    }

    public static void main(String[] args) {
        System.out.println(new So45012361Application().getType()); //class com.stackoverflow.So45012361Application$MeasurementsSet
        System.out.println(new So45012361Application().getType().getGenericSuperclass()); //java.util.HashSet<com.stackoverflow.So45012361Application$Measurement>
    }
}