Unit 8: ArrayList and Collections

Unit 7 ended with a structure that could not change size and a written note about what that cost. This unit pays that debt. It covers why the array ran out of room, the first ArrayList, why a list will not hold a plain int, add, get, set and remove, walking the whole list, the list methods students will actually use, counting the work instead of guessing it, what each structure costs and how to choose, searching a list two ways, sorting a list, and holding objects of a class the student wrote.

The performance task is The Roster That Grows. Students rebuild a Unit 7 problem so that the part that changes size becomes an ArrayList while the fixed part stays an array, and say in one sentence why. They add a counter to their own code and fill in a cost table at list sizes of at least ten, one hundred and one thousand for at least three operations, including add at the end, insert at the front and find an item, then write a comparison of at least 250 words. The comparison must name one job the ArrayList made harder or slower, because there is one.

The heaviest criterion is that the comparison is carried by counted evidence: a claim with no number behind it earns nothing however true it sounds, and a student who predicted one result, measured another and reported the measurement honestly earns full credit. Sorting a list of the student's own objects by a chosen field is named as a real limitation and handed to Unit 9. A teacher gets a plan and a substitute plan for each of the fifteen lessons, answer keys, tiered handouts, and the cost table with worked teacher numbers.

The unit runs 15 instructional days.