Lesson 5: Lists of Objects

We have worked with 1D and 2D arrays in previous units and have been learning about ArrayLists over the last few lessons. While an ArrayList allows us to store a list of data similar to a 1D array, it has additional capabilities that make it more flexible than a 1D array. It also uses a different syntax than a 1D array.

Discuss: Click through the animated slide to display the prompts. Use the Retrieve-Pair-Share strategy to discuss the prompts.

• What is unique about the syntax of an ArrayList?
• What do you think is the purpose of the angle brackets < >?

Discussion Goal: Students note that the angle brackets < > are unique to ArrayLists. Students recall that the type of data the ArrayList can store is specified inside the angle brackets and guess that the purpose of the angle brackets is to specify the reference type.

There is a reason why an ArrayList uses this syntax. We have learned that an ArrayList can only store objects, like Integer, Double, String, and any other object we choose.

Do This: Review the lesson objectives.

Group: Place students in pairs.

Do This: Direct students to Level 1 on Code Studio to investigate the program with a partner. Students make the changes to the program as prompted.

Discuss: Click through the animated slide to display the prompts.

• What do you notice about the code in this program?
• What do you wonder about the code in this program?

Discussion Goal: Students notice that an ArrayList can store objects like a 1D and 2D array. Students also notice that an ArrayList can be declared and initialized without the < > but doing so allows the ArrayList to store objects of different and unrelated types. Students may wonder why the < > are used instead of the [ ] and why omitting the < > allows the ArrayList to store different and unrelated objects.

Do This: Click through the animated slide to define generic type and explain the functionality of ArrayList<E>.

We have developed and reused standard algorithms to work with 1D and 2D arrays to solve different types of problems. Let’s combine our knowledge of standard algorithms with what we’ve learned about ArrayLists.

Do This: Direct students to Level 2 on Code Studio to complete Levels 2 and 3. On Level 2, students translate the given code with a 1D array to an ArrayList. On Level 3, students complete a choice level to apply standard algorithms to an ArrayList.

Do This: Click through the animated slide to have students participate in the Code Review Call and Response.

Do This: Direct students to complete a code review on Level 4.

We have learned a lot about ArrayLists and applying standard array algorithms to ArrayLists. Let's recap some of the key concepts we have learned.

Discuss: Click through the animated slide to display the prompts.

• When is it best to use an ArrayList instead of a 1D array?
• How is applying standard algorithms to an ArrayList similar to a 1D array? How is it different?
• What were you confident about in this lesson? What would you like to practice?

Discussion Goal: Students share scenarios where an ArrayList is best, such as when the size of the list is unknown and may change. Students identify similarities and differences between applying standard algorithms to an ArrayList and a 1D array, such as using the same steps but different syntax. Students share concepts they are confident about and that they need more practice.

Do This: Review the concepts covered in this lesson.

Display: Key Vocabulary

Check For Understanding Question(s) and solutions can be found in each lesson on Code Studio. These questions can be used for an exit ticket.

To assign questions from the AP Classroom Question Bank that align with this lesson, create a custom quiz in AP Classroom by searching the Question Bank for the Essential Knowledge statements listed at the top of this lesson plan. You can find instructions and video demonstrations to do this on AP Central.

The following Topic Questions in AP Classroom can be assigned as a formative assessment for this lesson:

• Topic Questions 7.1

Note: Some Learning Objectives and Essential Knowledge statements in the suggested Topic Questions are covered in later units.