Lesson 8: More Array Algorithms

while loops and for loops are helpful for repeating a task and for traversing a 1D array.

Discuss: How could we achieve this using a while loop? How could we achieve this using a for loop?

Discussion Goal: With a while loop, the Painter object can be moved from (2, 5) to (2, 1) by moving forward until it is on a paint bucket. This condition can be checked using the isOnPaintBucket() method. With a for loop, the Painter object can be moved from (2, 5) to (2, 1) by moving four times.

As software engineers work with larger amounts of data, they often need to store the information in other files to read into their programs.

Do This: Review the lesson objectives.

Do This: Direct students to Level 1 on Code Studio to predict the program's outcome, then run the program to compare their predictions to the actual outcome.

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 values are stored in a text file and read into the program. Students also notice that the values are stored in a 1D array. Students may wonder how they might work with larger files or with multiple types of values or how they could write data to a file.

Do This: Click through the animated slide to introduce the File class.

When introducing the File class, focus on the File(String pathname) constructor. In Java Lab, students can create a File object by specifying the name of the text file as a String.

Do This: Define text file.

Ask students if they have used a text editor such as Notepad. Have students identify the similarities and differences between the files created in these text editors and programs like Microsoft Word or Google Docs.

Discuss: Use the Hold That Thought strategy to discuss the prompt.

• How can reading a file be useful in a program?

Discussion Goal: Students note that a program can read data in a file. Students may also suggest that it makes the program more user-friendly and adaptable. The user does not need to enter the files directly into the array, and one program can process multiple data sets.

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

• What do you notice about the packages that are imported? Why do you think we need these?
• What do you think the instance variables represent?

Discussion Goal: Students identify the packages that are imported and predict that these are needed to provide access to the Scanner, File, and FileNotFoundException classes. Students note that the instance variables represent a Scanner object to read the file and a File object for the file.

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

• What do you notice about the constructor?
• What do you think is the purpose of the setFile() method?

Discussion Goal: Students notice that the constructor calls the setFile() method. Students realize that the setFile() method instantiates the File and Scanner object. Students note that this method is a mutator method so it can be used to change the file and update the Scanner object to read a different file.

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

• What do you think is the purpose of the createScanner() method?
• What do you notice about the code in this method?

Discussion Goal: Students note that the method returns a Scanner object to read the file. Students notice that the code uses a try/catch block that instantiates the Scanner object or notifies the user that the file cannot be found if a FileNotFoundException occurs.

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

• What do you think is the purpose of the getIntData() method?
• How is this similar to how we have read input from a user? How is it different?

Discussion Goal: Students note that the method returns a 1D array of int values. Students realize that the Scanner object is used to check if there is a value to be read and reads the value into the array if a value is found. Students notice that the contents of the file are read using the same methods that they used to read user input, but that it first checks if there is data to read.

Students are not expected to know how to write code to read files on their own. Any activities in the curriculum that use file input provide the code for reading a file to students. The purpose here is to expose students to the functionality of the code so they understand how to use it when it is provided to them in upcoming activities.

Do This: Click through the animated slide to introduce the Scanner class methods for checking if there is input.

Files makes it easier for programs to apply the same algorithms to multiple data sets. This makes the program more flexible, but it also makes it more user-friendly because the user can just provide a different file to process and analyze using the same program.

Group: Place students in pairs.

Do This: Direct students to Level 2 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 is causing this error? How do we fix it?
• What are strategies we can use when debugging errors like this?

Discussion Goal: Students note that the program had an ArrayIndexOutOfBoundsException because the array traversal looped one too many times. Students share that changing the condition resolved the error and allowed the program to function as expected.

When we are using for or while loops, we need to be sure that these iteration statements do not loop one time too many or one time too few. Doing so results in an off-by-one error.

Do This: Explain off-by-one errors.

We have written algorithms throughout the unit to determine if elements in an array met specific criteria or find the sum or average of the values. We can also write algorithms to find the minimum and maximum values in an array.

Group: Place students in pairs.

These can be the same pairs as the previous activity.

Do This: Have students write pseudocode to find the minimum and maximum values of a 1D array.

Do This: Direct students to Level 3 on Code Studio to implement their algorithms.

We have learned a lot in this unit about storing values in 1D arrays and writing algorithms to find information.

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

• What was awesome about writing your code?
• What is one action you can take to improve your code?
• What questions do you have about today?

Discussion Goal: Students share aspects of their program they enjoyed or strengths of writing algorithms and identify areas of improvement to strengthen their programming skills. Students also share any questions or misconceptions they may have.

Glows, Grows, Want-to-Knows is a strategy to help students identify their strengths and areas of improvement and share any questions or misconceptions.

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 6.4

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