How to access private inner class using reflection?

How to insert or retrive values from this map? How to access private inner class using reflection?

public class Sample {
    private ConcurrentHashMap<String, TestPojo> testHash;

    private class TestPojo {
        ...
    }

    public ConcurrentHashMap<String, TestPojo> getTestHash() {
        return testHash;
    }
}


Class<?> noparams[] = {};
Method m = MainObj.getInstance().getSample().getClass().getDeclaredMethod("getTestHash", noparams);
ConcurrentHashMap<String, TestPojo> testMap = (ConcurrentHashMap<String, TestPojo>) m.invoke(MainObj.getInstance().getSample()); //Cannot use private class object here

//Tried the following as well:
ConcurrentHashMap<String, Sample> testMap = (cast) m.invoke(obj); //parent class of private inner class