Reuse an ordinary object

Your goal is to reuse ScoreDisplay and explain the difference between owning a number and displaying it.

Back up lesson 1 outside src/. Copy practice Main and shared ScoreDisplay into src/main/java/, following the switching steps. Keep the shared source unchanged for the first part of this lesson.

Predict the displayed count after Complete, Complete, Reset, Complete. Run the tracker and check for 1, 2, 0, 1. The button's full label is “Completed an exercise”.

Read completeExercise() and resetProgress() in Main. Main changes completed and then asks the display to show it. ScoreDisplay does not count exercises.

score = new ScoreDisplay("Completed");
score.setScore(completed);

Find the constructor that stores the caption and creates a Label. Find view(): it returns the label so Main can put it in a VBox. ScoreDisplay is an ordinary class, with no Zero parent class or registration step.

The quiz uses new ScoreDisplay(). Its no-argument constructor calls this("Score"), preserving the quiz's caption. Each app creates its own display object; one JavaFX node cannot belong to two different parents at once.

1. In practice Main, make each click count two completed exercises and change the button label to describe that rule. Leave ScoreDisplay unchanged.
2. Check two clicks, Reset and one click: expect 2, 4, 0, 2.
3. Back up the working tracker. In your copied src/main/java/ScoreDisplay.java, change the display format from Completed: 2 to Completed = 2. Update both the initial Label text and setScore() so the format is consistent at zero and after changes. Keep both constructors and method signatures.
4. Keep that modified display in place. Copy only the original quiz Main into src/main/java/Main.java. Run it: expect Score = 0, then Score = 10 after answering 42. Restore your tracker Main and check Reset again.

Your experiment is in your compiled copy. Keep the original example shelf intact so later lessons can copy its baseline. Save the modified class outside src/ before switching to another example. A proposed shared contribution needs review before replacing the canonical example source.

Show the same modified class working in the quiz and tracker. Identify one change that belonged in Main and one that belonged in ScoreDisplay. Explain why removing the no-argument constructor would break the quiz. Record both initial and changed display results, including Reset.