Any help?

Question about the task

Under discussion

I'm pretty sure, that the answer is LinkedList, but I have no clue hot to get that class name by using getDeclaredClasses. I would appreciate any tip.

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.
Using reflection (getDeclaredClasses method), return the appropriate type in the getExpectedClass method.

Requirements:

The getExpectedClass method must use the appropriate utility class's getDeclaredClasses method.
The getExpectedClass method must return the correct type.
The main method must call the getExpectedClass method.
The main method must display the returned class on the screen.

package com.codegym.task.task36.task3602; import java.util.ArrayList; import java.util.Collections; import java.util.LinkedList; import java.util.List; /* Find the class by its description */ public class Solution { public static void main(String[] args) { System.out.println(getExpectedClass()); System.out.println("****"); for(Class clazz : List.class.getDeclaredClasses()){ System.out.println(clazz); } System.out.println("DEC: "+ LinkedList.class.getDeclaringClass()); } public static Class getExpectedClass() { return Collections.class.getDeclaredClasses()[0]; } }

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Wei Cui

Level 39 , Newark, United States

21 April 2020, 16:46

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

    public static Class getExpectedClass() {
        for (Class clazz : Collections.class.getDeclaredClasses()) { //get classes
            for (Class interf : clazz.getInterfaces()) {
                if (interf.getSimpleName().equals("List") && Modifier.isStatic(clazz.getModifiers())) {
                    try {
                        return Class.forName("java.util.Collections$EmptyList");

                    } catch (ClassNotFoundException e) {
                        e.printStackTrace();
                    }

                }
            }
        }
        return null;
    }
}

Seb

Level 41 , Crefeld, Germany

23 February 2020, 12:41

Use your for loop from lines 16 to 18 in the getExpectedClass method. Then check for each class if it is private, static and implements the List interface. Something like if (Modifier.isPrivate(clazz.getModifiers())) { // only private classes if (Modifier.isStatic(clazz.getModifiers())) { // only static classes if (List.class.isAssignableFrom(clazz)) { // only classes that implement the List interface Now you can proceed to get a constructor for a class that fulfills all the above requirements. Once you've got the constructor (use reflection), you can construct a class and try to access an element via get, which should lead to an IndexOutOfBoundsException: List list = (List) constructor.newInstance(); list.get(0); The class that now throws the IndexOutOfBoundsException, should be the class that ought to be found - and can thus be returned. Good luck. P.S.: In case there are any further issues, you're welcome to message me directly.