Java Reflection API example

scratch_7.java

// Do not remove imports
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.WildcardType;
import java.util.Set;
import java.util.Scanner;

class ListParameterInspector {
    // Do not change the method
    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        String methodName = scanner.next();

        ListParameterInspector inspector = new ListParameterInspector();
        inspector.printParameterType(new TestClass(), methodName);
    }

    public void printParameterType(TestClass obj, String methodName) throws Exception {
        Method method = obj.getClass().getDeclaredMethod(methodName);
        ParameterizedType param = (ParameterizedType) method.getGenericReturnType();
        WildcardType wild = (WildcardType) param.getActualTypeArguments()[0];
        System.out.println(wild.getUpperBounds()[0].getTypeName());
    }
}

class TestClass {

    public Set<? extends ClassB> someMethod() {
        return Set.of(new ClassC(), new ClassB());
    }

}

class ClassB {

}

class ClassC extends ClassB {

}