Confusion with lists in the IB Computer Science syllabus

There are three key mentions of the word list in the IB syllabus and they are all HL only:

  • Linked lists in Topic 5
  • ADT list in Option D
  • ArrayList and LinkedList in Option D

Topic 5 Linked Lists

This reference is all about how linked list objects work with references to the next node. You need to be able draw or construct simple code to show the changes that the list undergoes with insertion or deletion of a node. You should also certainly know the basic algorithm for traversing the list, e.g searching for an item within it.

Types of lists are singly-linked, doubly-linked, circular, etc, and a key point is that they only support serial access and, unlike arrays, don’t support direct access.

ADT list in Option D (D4.7)

ADT stands for Abstract Data Type. The “abstract” is there because we are not worrying at all about implementation, just what operations a list might support. What the IB wants you to understand here is that we can still talk about adding, removing, getting the next value, etc, without specifying exactly how the data is stored. In the past there have been questions that invent a list, along with the operations it supports, there and then on the question paper, and students are expected to construct code using the list.

You can look at abstract lists in Java using the two links below. You are certainly not expected to know the details of these classes/interfaces, you just need the general concepts mentioned above.


ArrayList and LinkedList (D4.11)

The syllabus says you should have a “broad understanding of the operation of these lists and their interface (methods)”. Oddly you are not expected to know the implementation, but it seems to me a key fact that the underlying data structure in an ArrayList is an array, and the underlying data structure in a LinkedList is, well, a linked list. This has great implications for the decision as to which to select. Anyway, have a brief look at the Javadoc pages linked above, and also looked at the new slide put into the Option D presentation showing techniques for iteration through each of these list types.

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