I don't understand the solution. Why does it try to see if the clazz simple name is EmptyList ? What kind of class is this?

Question about the task

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I don't understand line 8.

public class Solution {
    public static void main(String[] args) {
        System.out.println(getExpectedClass());
    }

    public static Class getExpectedClass() {
        for (Class clazz : Collections.class.getDeclaredClasses()){
            if (clazz.getSimpleName().equals("EmptyList")){
                return clazz;
            }
        }
        return null;
    }
}

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Thomas

Level 41 , Bayreuth, Germany

21 July 2021, 15:21

solution

I just can read that as task description so most of my thoughts are assumptions Class description: 1. It implements the List interface; 2. It is a private static class inside a popular utility class; 3. Accessing the list by index is not allowed. It throws an IndexOutOfBoundsException. And I also assume the loop is given code CG assumes that you find the searched class by yourself (using some reflection magic or by just checking the classes Collections.class.getDeclaredClasses() spits out -> sources). Then there just one problem remains. You're not able to get the Class object of the result (EmptyList) as it is a private inner class (and that's why you also can not instanciate an object of the class itself and use getClass()). So they loop over all the class objects the Collection class declares. So the class objects now are accessible for you to return. You just need to grab the EmptyLists class object and return it. Hence the getSimpleName().equals("EmptyList"). A disappointing solution. Instead of comparing the simpleName you also could do some reflection checks. If the modifier is private and static (Modifier.isStatic(clazz.getModifiers()) or clazz.getModifiers() == Modifier.PRIVATE) Then check List.class.isAssignableFrom(clazz) // no.1 of the requirements now you could try to get the constructors and then make the constructor accessible (cause it is private with setAccessible(true) However I have a problem with that as this seems only to work till Java 8. I'm not sure about that though. At least with my Java 16 I get exceptions ;) With that accesible constructor you can instanciate an object of that class and try to access the object (list) with an index. That's no. 3 of the requirements. If the IndexOutOfBoundsException is triggered you can return the clazz as your solution.

Andrei

Level 41

21 July 2021, 15:59

Search for a class by its description Replace the following words with those required: 1. ClassNameToBeReplaced - the name of a class that is a thread-safe version of ArrayList, in which all change operations (mutative operations) use a new copy of the original array. 2. methodNameToBeReplaced - the name of a method that adds to the current "list" the elements of the passed collection that aren't in "list". Don't leave commented code. Requirements: 1. The main method must create a thread-safe version of ArrayList as outlined in the task conditions. 2. After creating the correct type of list, the main method must call a method that will only add to the current "list" the elements of the passed collection that aren't in "list". 3. The program must display 4 strings: "A C B D". 4. The program must not contain the words "ClassNameToBeReplaced" and "methodNameToBeReplaced".

Andrei

Level 41

21 July 2021, 16:00

These are the requirements. Why do you think it is disappointing? I think it is very simple and elegant. So basically there is actually such a class EmptyList, I see.

Thomas

Level 41 , Bayreuth, Germany

21 July 2021, 16:52

As said, I expected them to use (pure) reflection to get that EmptyList class and not just hardcoding the searched class name into the code. Like the solution I've outlined above. However the problem (I guess) was that you can not use forName on a private inner class. And I was close with my guess to what CG is asking ;) Edit: And I see you're lvl 36 now... congrats :)

Andrei

Level 41

21 July 2021, 16:56

Thanks! 😁 after level 30, levels seem shorter tbh, I am going I think twice as fast as I was going through multithreading. But I am also focusing only on CG so I can finish faster and start working on my portfolio so I can get a job. 😁