Lessons
Start
Start learning
CodeGym /Courses /Java Collections /Big task: AbstractList class

Big task: AbstractList class

Java Collections
Level 1 , Lesson 15
Available

"Hello, soldier!"

"Congratulations on upgrading your skills. We need guys who are prepared to do anything."

Kotlin

"I'm sure you still have many unfinished tasks. It's time to finish some of them!"

14
Task
Java Collections, level 1, lesson 15
Locked
Build a tree (part 1)
Build a tree (part 1)
Open
14
Task
Java Collections, level 1, lesson 15
Locked
Build a tree (part 2)
Build a tree (part 2)
Open
14
Task
Java Collections, level 1, lesson 15
Locked
Build a tree (part 3)
Build a tree (part 3)
Open
28
Task
Java Collections, level 1, lesson 15
Locked
Build a tree (part 4)
Build a tree (part 4)
Open
28
Task
Java Collections, level 1, lesson 15
Locked
Build a tree (part 5)
Build a tree (part 5)
Open
Comments (20)
TO VIEW ALL COMMENTS OR TO MAKE A COMMENT,
GO TO FULL VERSION
Azamjon Sobirov Level 47, Toshkent, Uzbekistan
12 June 2025
part 5 is very horrible
Evgeniia Shabaeva Level 42, Budapest, Hungary
29 May 2025
It was interesting to use Queue in the last task, I hope I got it. Somehow I passed the last two tasks, even though the output for the "16" node remained wrong all the way. |Still, the solutions got validated. Can't complain, but I'm somehow worried that I missed learning something I should have.
cute potato Level 46, Poland, Poland
4 February 2023
Like without explanation about the tree data structure you give such hard tasks? Gosh...
Justin Smith Level 41, Greenfield, USA, United States
17 August 2022
This was hard, but really cool. Step 4 is by far the hardest leap in logic, but once you have gotten there, Step 5 is just a continuation of that logic and not terribly hard in itself.
Lisa Level 41
11 December 2021
I just read a book about data structures and a huge part of it was about trees (needed 5 or 6 weeks for that). Without that knowledge I'm 100% sure that I never would have been able to solve this task.
matemate123 Level 50, Kraków, Poland
24 August 2023
Can you tell us what title this book has?
Jurij Thmsn Level 29, Flensburg, Germany
24 May 2021
Nice tasks! Hard, but doable without having to google any new classes etc. Just used ArrayLists, Queues and a lot of if-statements. And a commented "right solution" - finally! (even though I don't really understand it 😬)
MaGaby2280 Level 41, Guatemala City, Guatemala
19 May 2021
Wow! These task really hurt my brain... there should be a better explanation for part 4 and 5!
joe Level 27, London, United Kingdom
19 January 2021
Really need some explanation for parts 4 and 5. Like BlueJavaBanana said there's a ridiculous difficulty jump from parts 1 to 3. "do a little work on your own" I laughed .........
LennyMan Level 25, Lucca, Italy
13 January 2021
Someone can please explain what happen here: private transient ArrayList<Entry<String>> queue; Is it in the solution of the part4
BlueJavaBanana Level 37
3 January 2021
Dreadful task. Part 1,2,3 are a joke easy. Then boom make the tree logic with zero clues as to how they might want you to solve it. Got a working solution? Well too bad the validator don't wanna know!
Romain Level 26, Paris, France
15 March 2021
I thought it too, but when you understant you just need to add a list in your customTree class, it becme easy. ^^