be sure that the removeAllNumbersGreaterThan10 method works with sets of any size.?

Question about the task

Greater than 10? You're not a good fit for us

Java Syntax, Level 8, Lesson 8

Resolved

Could anyone tell me what i am doing wrong? The issue is in the loop, but I just assume it can work on any set size.

package com.codegym.task.task08.task0814; import java.util.HashSet; import java.util.Set; /* Greater than 10? You're not a good fit for us */ public class Solution { public static HashSet<Integer> createSet() { // write your code here HashSet<Integer> mySet = new HashSet<Integer>(); for(int i = 0; i < 20;i++){ mySet.add(i); } return mySet; } public static HashSet<Integer> removeAllNumbersGreaterThan10(HashSet<Integer> set) { // write your code here for (Integer number : set) { if (number > 10) { set.remove(number); } } return set; } public static void main(String[] args) { } }

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Norbert

Level 9 , Krakow, Poland

28 April 2020, 11:56

You can read more about the topic that Guadalupe gives https://codegym.cc/groups/posts/20-deleting-an-element-from-an-arraylist or here: https://codegym.cc/groups/posts/198-how-to-use-a-java-iterator-a-brief-tutorial

Lgd

Level 20 , London, United Kingdom

17 March 2020, 10:43

Guadalupe...many thanks for your ongoing contributions. Really very helpful. thanks

Guadalupe Gagnon

Level 37 , Tampa, United States

8 April 2019, 01:51

solution

You cannot remove items from a set in a foreach loop. It will screw up the internal order and you end up with a ConcurrentModificationException and subsequent crash. You need to create an Iterator:

Iterator<Integer> itr = *Set*.Iterator();

**Notice that Set is capitalized, that is because you can use this with any set type (HashSets, LinkedHashSet, TreeSet) as well as Maps and Lists. Make sure that you do not type 'Set' like above, but the actual variable that is of Set (or other) type.*** Inside the angle bracket needs to be the same base type as the set (or other) that you are going to iterate through, in this case Integer. You can name it anything, i used itr, short for iterator. Then set it equal to the Iterator() method of the set you want to iterate through. Then to iterate you use a while loop and call itr.hasNext() (which returns true if there are still values left to iterate through, or false otherwise). Then you can call itr.next() to pull the next value, check if is greater than 10, and remove it SAFELY with itr.remove();

while(itr.hasNext())
   if(itr.next() > 10)
      itr.remove();

+20

Serg

Level 17 , Minsk, Belarus

22 May 2019, 19:41

i solved this task in such manner in my IDEA: /* for(int i = 0; i < set.size(); i++){ if(set.contains(i+11)){ set.remove(i+11); } */ ...but this method failed the CC validation ;(

Guadalupe Gagnon

Level 37 , Tampa, United States

22 May 2019, 20:36

@serg The problem with that code it is that it will not remove all the numbers from a random set of numbers, it only works with the set that you create and then pass. What if another programmer used you code that is supposed to remove all numbers greater than 10 and passed it a set of 20 numbers that were: [1,2,3,4,5,6,7,8,9,10,100,200,300,400,500,600,700,800,900,1000] That code would not remove a single item. Now if you are commenting about the for loop you used, that is not a foreach loop. If you did a foreach loop with that code then you would get a concurrent modification exception thrown if any value is removed.

Serg

Level 17 , Minsk, Belarus

23 May 2019, 12:07

- thanks, i see, the logic in my example is wrong. I can only check the specific value(with "contains"), but i can't compare values between each other( ">, <, ="). Maybe it real in for( ; ; ) loop with the comparator or something else, but i haven't read it yet about. I simply tried to deceive the CC validation :);

Guadalupe Gagnon

Level 37 , Tampa, United States

23 May 2019, 13:31

Trying a whole bunch of ideas (and subsequently failing a lot of them) is the best way to learn programming. I came up with so many different 'solutions' to the problems when I was first learning, and i use the term 'solution' loosely. You will learn to start letting go of assumptions and programming dynamically to catch any problems that could arise. A task will have you figuring out how to find the minimum of three ints and you will write code that not only does that but could also find the minimum of any amount of numbers with almost limitless values. It takes time, and a lot of patience, but you will get there. I bet all the tasks from levels 2-5 look like a walk in the park now to you, and when your are nearing level 20 all the tasks below 15 are going to look easy. Good luck to you on your continued learning!

Serg

Level 17 , Minsk, Belarus

23 May 2019, 14:53

Thank you, it's all true! Very motivating speech!

Alesha Ray

Level 20 , Austin, United States

30 August 2019, 23:51

Thanks for your help with this @Guadalupe Gagnon. I'd used iterators before and knew my code was correct but when the lesson said that it only had two methods (next and hasNext), I completely forgot that you could call remove on the iterator. I kept calling remove on set and was getting so bothered because I knew my code should be working. Thanks again.