Java Practice It | Exercise 16.9: stutter | LinkedLists, #implementing instance methods

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Problem:

Question:
Write a method stutter that doubles the size of a list by replacing every integer in the list with two of that integer. For example, suppose a variable list stores the following sequence of integers:

[1, 8, 19, 4, 17]

[1, 1, 8, 8, 19, 19, 4, 4, 17, 17]
Assume that you are adding this method to the LinkedIntList class as defined below:

public class LinkedIntList {
private ListNode front; // null for an empty list
...
}