Question

I found i have problems when reflecting on a method with generic type paremeter, but the same code works fine with method without generic type paremeter! Here’s my code :

public class Test {

    public static void method1(Integer i) {
    }

    public static void method2(List<Integer> i) {
    }

    public static void main(String[] args) throws Exception {

        Integer i = 5;
        List<Integer> iList = new ArrayList<Integer>();
        Method method1 = Test.class.getDeclaredMethod("method1", i.getClass());
        method1.invoke(Test.class, i);
        System.err.println("-------- method 1 ok -----------");
        Method method2 = Test.class.getDeclaredMethod("method2", iList.getClass());
        method2.invoke(Test.class, iList);
        System.err.println("-------- method 2 ok -----------");
    }

}

And the output:

-------- method 1 ok -----------
Exception in thread "main" java.lang.NoSuchMethodException: 
Test.method2(java.util.ArrayList)
    at java.lang.Class.getDeclaredMethod(Class.java:1954)
    at Test.main(Test.java:24)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)

Is there anything magic with generic type paremeter ??

Answer 1

ArrayList is too specific, you’ve only defined method2 as taking a List (as you generally should).

Try with List.class