Lab B Working with Classes (Point + Circle)

Overview · Learning Goals · Files Provided · How to Test · Specifications · Constraints · Checklist · Submission · Grading

Overview

In this lab you will implement two small Java classes that model objects and their relationship: Point and Circle. This lab focuses on class structure and core object-oriented programming fundamentals.

Learning Goals

• Declare and use private instance variables
• Write overloaded constructors
• Use constructor chaining with this(...)
• Implement getters and setters
• Use composition (a Circle has a Point)
• Implement and reuse toString()
• Use a private helper method for validation
• Test classes using separate driver programs

Files Provided

Download all four files and place them in the same directory.

Classes to Implement

• Point.java
• Circle.java

These files contain Javadoc and TODO: comments. Complete the TODOs while keeping the required method signatures intact.

Basic Lab Testers (Self-Check)

• PointTester.java (basic checks for development and debugging)
• CircleTester.java (basic checks for development and debugging)

The testers check several specific parts of your implementation and can help you identify common problems while you work.

How to Test

Compile your classes and the provided testers from the same directory. Run each tester as you work to check specific parts of your implementation.

Compile

javac Point.java Circle.java PointTester.java CircleTester.java

Run the Basic Testers

java PointTester
java CircleTester

Run the testers as you work. Any FAIL messages can help you identify problems in your implementation.

Specifications

Class: Point

A Point represents a location in 2D space.

• Stores an x coordinate (double) and a y coordinate (double)
• All instance variables must be private
• Constructors:
  • Point() initializes to (0.0, 0.0) and must delegate using this(...)
  • Point(double x, double y)
• Methods:
  • Getters and setters for both coordinates
  • toString() must return exactly: (x, y)

Use PointTester.java to test constructors, getters, setters, and toString().

Class: Circle

A Circle is defined by a center point and a radius.

• Stores a center (Point) and a radius (double)
• All instance variables must be private
• Constructors:
  • Circle() initializes to center (0.0, 0.0) and radius 1.0, and must delegate using this(...)
  • Circle(Point center, double radius)
  • Circle(double x, double y, double radius)
• Radius rule: the radius must never be negative
• Negative radius values must be handled using a private helper method
• Methods:
  • Getters and setters for center and radius
  • toString() must return exactly:

    Center: (x, y), Radius: r

Use CircleTester.java to check constructors, radius validation, setters, and required observable output.

Implementation Constraints

• Do not add main methods to Point or Circle
• Do not print anything from inside Point or Circle
• Do not use static instance variables
• Do not change method signatures
• Default constructors must use this(...) to avoid duplicate initialization code
• All instance variables must be private
• Validation logic must be placed in private helper methods

Testing Checklist

• Point.java and Circle.java compile without errors
• You have run both basic self-check testers and investigated any failing checks
• Point() delegates using this(0.0, 0.0)
• Circle() delegates using this(...) rather than duplicating initialization
• Negative radius values are handled correctly so the radius never becomes negative
• Radius validation uses the required private helper method
• Circle.toString() obtains its center text by calling center.toString()
• You can explain how your constructors, setters, validation, and composition work

Submission

Navigate to your personal Google Drive folder for CS231 and open the Projects folder.

1. Create a new folder whose name matches the current project name.
2. Place your completed lab files for this week's work in that folder.
3. Before leaving lab, verify that the files are present in Google Drive.

For this lab, upload:

• Point.java
• Circle.java

Grading (High-Level)

• Correctness and adherence to the written specification
• Proper use of access modifiers
• Constructor chaining via this(...)
• Avoidance of duplicate initialization logic
• Correct delegation between objects (Circle → Point)
• Code clarity and organization