Java Bootcamp – Workbooks and Challenges

Quidditch – Part 2

Goal: Quality control the Team class.

Unchecked exceptions

An unchecked exception crashes the app as a result of badly written code.

You should throw an:

  • IllegalArgumentException when the caller passes faulty arguments into a method/constructor.

  • IllegalStateException when an object calls its method at a "bad time" (object not in a legal state).

Throwing an unchecked exception forces the caller to improve their code.

Task 1 – Team Constructor

In the Team constructor, throw an IllegalArgumentException if:

  • any of the fields are null.

  • any of the String values are blank.

  • chasers length not equal to 3.

Task 2

1. Create a test that fails

Write a unit test named hasNullTest. The test defines the following array. Then, use assertTrue to check if the array hasNull.

String[] chasers = new String[] {null, "Ginny", "Katie"});

Inside, write code to make the test fail. Make the method static because it doesn't interact with any fields. By making it static, it belongs to the class, so you can call it directly from the class.

/** * Function name: hasNull * @param array * @return (boolean) * * Inside the function: * 1. return false; */

2. Make the test pass

Inside the function, use a for loop that runs through the length of the parameter. return true if any element is null.

3. Refactor

Screen Shot 2021-07-13 at 2.25.19 PM.png

  1. You can pass regular arrays into an pipeline.

  2. anyMatch is a terminal operation that returns true if ANY element matches the predicate, and false otherwise.

4. Refactor

Refactor if necessary.

Task 3

1. Create a test that fails

Write a unit test named hasBlankTest. Inside, use assertTrue and call hasBlank to assert the array below has a blank field:

String[] chasers = {" ", "Ginny", "Katie"};

Then, write code to make the test fail.

/** * Function name: hasBlank * @param array * @return (boolean) * * Inside the function: * 1. return false; */

2. Make the test pass

See Task 2.

3. Refactor

Refactor if necessary.

Task 4

Inside the constructor, throw an IllegalArgumentException if an array hasNull or hasBlank.

Task 5

Apply the same quality control inside every setter. Use the following function for setHouse, setKeeper, and setSeeker:

public void checkParam(String param) {
    if (param == null || param.isBlank()) {
        throw new IllegalArgumentException(param + " cannot be null or blank");

Final Remarks

  • You added checkpoints to the Team class. Each checkpoint forbids the caller from misusing the methods/constructor.

  • You unit tested two methods. Each method is modular and free of bugs.

Screen Shot 2021-07-13 at 3.58.46 PM.png

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