Lesson 7: Writing Methods

Discuss: Click through the animated slide to display the prompts. Use the Hold That Thought strategy to discuss the prompts.

• Do all birds have the same attributes and behaviors as a Bird?
• Do these birds have additional attributes and behaviors?
• Should these additional attributes and behaviors be accessible by the Bird class?

Discussion Goal: Students note that all members share the same attributes and behaviors as a Bird since they extend the Bird class. Students suggest that some of the members might have additional attributes and behaviors depending on the type of bird. Students realize that these additional attributes and behaviors shouldn't be accessible by all birds, such as the ability to fly.

Software engineers often create subclasses to have additional methods or attributes. We created a PainterPlus class to have a new type of Painter with additional behaviors. Before adding new methods to the PainterPlus class, we need to know how to write a method.

Do This: Review the lesson objectives.

Display: Show the video – Writing a Method.

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

• What does it mean for a method to be a void method?

Discussion Goal: Students recall that a void method does not return a value and only performs a specified action.

Have students look at the methods on the UML diagram for the Painter class and identify the methods that are void. Ask students what these methods have in common.

Do This: Review the void keyword.

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

• What are the similarities and differences between calling methods and writing methods?

Discussion Goal: Students recall that they call a method by specifying the name of the object followed by a dot then the name of the method. Students note that this calls a method that is already in the class. Students share writing a method requires providing a method signature and the block of code that the method executes when it is called.

To help students identify similarities and differences, make the analogy that writing a method is like writing a recipe while calling a method is like cooking the recipe.

Do This: Review how to call methods and compare to writing methods.

Do This: Demonstrate how to write a new method in a class.

The Painter class doesn't have a method to turn right. Now we have a PainterPlus class that extends the Painter class.

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

• What does a PainterPlus object need to do to turn right? What would we write in the body of the turnRight() method?

Discussion Goal: Students suggest calling turnLeft() three times in the body of the turnRight() method.

Do This: Have students add the turnRight() method to the PainterPlus UML diagram.

Let's add this new method in the PainterPlus class to allow PainterPlus objects to turn right.

Do This: Direct students to Level 1 on Code Studio to complete Levels 1, 2, and 3. Students write the turnRight() method in their PainterPlus class, then use the turnRight() method on Level 2. Students debug the program on Level 3 that attempts to call turnRight() on a Painter object.

To help students recall errors during the wrap up, give each student several sticky notes and have them keep track of errors they encounter while they work.

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

• Why would we write a new method in the subclass instead of in the superclass?

Discussion Goal: Students recall the Painter class is part of The Neighborhood package, so they cannot modify it. Students note that if the method is only for one subclass and not a shared behavior for all types of objects, then it should not be added to the superclass.

Do This: Have students predict the outcome of the code segment. Click through the animated slide to explain that a superclass cannot use the methods in the subclass, but the subclass inherits methods from the superclass.

The Painter class cannot use any methods that are written in the PainterPlus class. Any method that is called must be defined within its own class or its superclass.

We saw some new types of errors today! Let's discuss these errors we encountered and update our Debugging Wall with the strategies we used to debug them.

Discuss: Click through the animated slide to display the prompts. Use the Hold That Thought strategy to discuss the prompts.

• What errors did you encounter while writing your code?
• How did you find and fix the error?

Discussion Goal: Students share examples of errors they encountered, including calling a subclass method on a superclass. Students suggest strategies for finding and fixing these errors.

Do This: Have students choose a strategy as a class and add it to the Debugging Wall.

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. You can use these questions as 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.