Unit 3 Practice: Java Class Creation

Name: ________
Unit: CS Awesome Unit 3 - Class Creation

Write every solution in Java. Run each problem in a separate file with public class Main. Declare class fields as private and provide behavior through methods when needed.

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Problem 1. Book Record Class

Write a BookRecord class that represents one book you have read.

Requirements

• Declare String title, String author, and int pages instance variables.
• Write a constructor that receives all three values.
• Write a getLabel() method that returns a string in this format: title - author (pagesp).
• In Main, create new BookRecord("Wonder", "R. J. Palacio", 315) and print the result of getLabel().

Sample Output

Wonder - R. J. Palacio (315p)

Check Your Work

• Do the class name and constructor name both use BookRecord?
• Are the fields used inside an instance method instead of being printed directly from Main?

Problem 2. Change an Object's State

Write an EventCounter class that tracks attendance at a school event.

Requirements

• Declare String eventName and int count instance variables.
• The constructor receives the event name and initializes count to 0.
• The add(int people) method increases count by people.
• The getCount() method returns the current attendance count.
• In Main, create a counter for Science Fair, call add(12) and add(8), then print the event name and count.

Sample Output

Science Fair: 20

Check Your Work

• Is add declared with the return type void because it changes state?
• Is getCount declared with the return type int because it returns a value?

Problem 3. Send a Score to Another Object

Write a program that compares the quiz scores of two students.

Requirements

• Create a StudentScore class with String name and int score fields.
• Its constructor initializes the name and score.
• Write boolean scoredHigherThan(StudentScore other). It returns true only when the current object's score is higher than other's score.
• In Main, create Mina(92) and Jisoo(87), then print mina.scoredHigherThan(jisoo).

Sample Output

true

Check Your Work

• Does the method parameter have the type StudentScore?
• Did you correctly use an instance variable from the parameter object, such as other.score?

Problem 4. Shared Library Member Count

Write a LibraryMember class that represents a library member.

Requirements

• Store a String name for each member.
• Declare one shared static int memberCount for all members.
• Increase memberCount by 1 every time the constructor is called.
• Write static int getMemberCount() to return the total number of members.
• In Main, create three members, then print the total number of members.

Sample Output

3

Check Your Work

• Is memberCount declared static so it is not duplicated for every object?
• Is the static method called as LibraryMember.getMemberCount()?

Problem 5. Manage a Card Balance with this

Write a TransitCard class for a simple prepaid transit card.

Requirements

• Declare String owner and int balance instance variables.
• Give the constructor parameters the same names, owner and balance, then use this.owner and this.balance to initialize the fields.
• The charge(int amount) method adds amount to the balance.
• The payFare(int fare) method subtracts the fare and returns true only when the balance is sufficient. If not, it leaves the balance unchanged and returns false.
• In Main, create new TransitCard("Alex", 1200), call charge(500) and payFare(1400), then print the remaining balance.

Sample Output

true
300

Check Your Work

• Does the constructor use this to distinguish fields from parameters?
• Does payFare return false without changing the balance when funds are insufficient?

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Reference: Runestone Academy, CSAwesome2 Unit 3: Class Creation