Java Reflection NoSuchMethodException when referencing a method in same class

Question

I am experiencing a NoSuchMethodException when trying to call getMethod on a method in the same class with no arguments from a string name pulled from a hashmap. Any advice, or another way to call a method in the same class given only a String name of the method? The call to get the method is here:

if (testChoices.containsKey(K)) {
        String method = testChoices.get(K);
        System.out.println(method);

        try {
            java.lang.reflect.Method m = TST.getClass().getMethod(method);
            m.invoke(testChoices.getClass());
        } catch (NoSuchMethodException e1) {
            // TODO Auto-generated catch block
            System.out.println("No method found");
            e1.printStackTrace();
        } catch (SecurityException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();


        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();

One of the methods I am trying to call is here:

private static void testgetDomainLic() throws IOException {

And the map entry being called is here:

testChoices.put(1, "testgetDomainLic");

Is the static method `testgetDomainLic()` defined in the TST class, or in a superinterface of it? — Andy Thomas, Jun 29 '17 at 14:36
TST is just an instance of the class where testgetDomainLic() is. — user8232299, Jun 29 '17 at 14:41
I changed it to call the directly defined class with Class.forName and it still is not finding the method. — user8232299, Jun 29 '17 at 14:53

score 0 · Answer 1 · answered Jun 29 '17 at 14:37

0

I'm not an expert, but try changing your method so it is not private.

Private methods can be invoked by reflection, but there are extra steps. See Any way to Invoke a private method?

answered Jun 29 '17 at 14:37

lego hazmat

1
3

1

The OP is getting a NoSuchMethodException. The problem is with `getMethod()` -- not with `invoke()`. – Andy Thomas Jun 29 '17 at 14:39
Also, I have tried removing the Private but it still gives the same error – user8232299 Jun 29 '17 at 14:42
OK. So I'm fixing the problem they haven't got to yet! – lego hazmat Jun 29 '17 at 14:44

score 0 · Accepted Answer · answered Jun 29 '17 at 15:10

I think in your case you can just change getMethod to getDeclaredMethod. getMethod only returns public methods.

The hiccup here is that they actually have different semantics other than whether or not they return non-public methods. getDeclaredMethod only includes methods which are declared and not inherited.

So for example:

class Foo { protected void m() {} }
class Bar extends Foo {}
Foo actuallyBar = new Bar();
// This will throw NoSuchMethodException
// because m() is declared by Foo, not Bar:
actuallyBar.getClass().getDeclaredMethod("m");

In the worst case like this, you have to loop through all declared methods, like this:

Class<?> c = obj.getClass();
do {
    for (Method m : c.getDeclaredMethods())
        if (isAMatch(m))
            return m;
} while ((c = c.getSuperclass()) != null);

Or accounting for interfaces (mostly because they can declare static methods now):

List<Class<?>> classes = new ArrayList<>();
for (Class<?> c = obj.getClass(); c != null; c = c.getSuperclass())
    classes.add(c);
Collections.addAll(classes, obj.getClass().getInterfaces());
Method m = classes.stream()
                  .map(Class::getDeclaredMethods)
                  .flatMap(Arrays::stream)
                  .filter(this::isAMatch)
                  .findFirst()
                  .orElse(null);

And as a side note, you probably don't need to call m.setAccessible(true), because you're invoking it from within the class that declares it. This is necessary, though, in other contexts.

Java Reflection NoSuchMethodException when referencing a method in same class

2 Answers2