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

Overview

In this project you will implement two Java classes that model objects and their relationship: Elephant and Tracker. Together, these classes represent a simplified park-tracking system where each elephant has a tracker that stores its distance from the center of a park.

Learning Goals

• Declare and use private instance variables
• Write overloaded constructors
• Use constructor chaining with this(...)
• Implement getters and setters
• Use composition (an Elephant has a Tracker)
• Implement and reuse toString() with a strict format
• Practice delegation (Elephant → Tracker)
• Maintain a class invariant (distance is never negative)

Files Provided

Classes to Implement

• Elephant.java
• Tracker.java

These files contain Javadoc and TODO: comments. You must complete the TODOs while keeping method signatures intact.

Provided Demo File (Read-Only)

• ElephantDemo.java

Optional Grader Tester (For You)

• ProjectBTester.java (for development / self-checking)

How to Test

This project includes a provided demo program that repeatedly moves a herd of elephants and prints their state. If your classes are correct, the demo will compile and run without errors.

Compile and Run

javac *.java
java ElephantDemo

If provided, you may also run the tester for a score-based self-check:

javac *.java
java ProjectBTester

Specifications

Class: Tracker

A Tracker stores and updates an elephant’s distance from the park center using the 1D distance model.

• Instance variables:
  • distance from center (kilometers)
  • park radius (kilometers)
• Constructors:
  • Tracker() places the elephant at the center and uses a default radius of 30 km
  • Tracker(double distanceFromCenter, double parkRadius)
• Methods:
  • Getters and setters for both instance variables
  • move(double x) randomly moves toward or away from the center by x km
  • isInsidePark() returns whether distanceFromCenter <= parkRadius
  • toString() must follow the strict format below

Class: Elephant

An Elephant stores biological information and owns exactly one Tracker. The elephant delegates movement and park-boundary checks to its tracker.

• Instance variables:
  • age (integer in the range [1, 60])
  • sex (character: 'm' or 'f')
  • a reference to a Tracker
• Constructors:
  • Elephant() assigns a random age in [1, 60], a random sex, and creates a default Tracker
  • Elephant(int age, char sex, Tracker tracker)
• Constructor chaining required: the default constructor must delegate to the full constructor using this(...)
• Methods:
  • Getters and setters for all instance variables (enforce valid age/sex)
  • move(double delta) delegates to the tracker
  • isInsidePark() delegates to the tracker
  • toString() must follow the strict format below

Strict toString() Format

Tracker.toString()

Must return exactly this style:

Tracker[distance=DIST km, radius=30.0 km, inside=BOOLEAN]

Note: DIST will vary (it is a number). BOOLEAN is either true or false.

Elephant.toString()

Must return exactly this style:

Elephant[age=AGE, sex=SEX, TRACKER_STRING]

Implementation Constraints

• Do not add main methods to Elephant or Tracker
• Do not print anything from inside Elephant or Tracker
• 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
• Invariant: distance from center must never be negative

Testing Checklist

• javac *.java compiles without errors
• ElephantDemo runs without crashing
• Default constructors delegate using this(...) (no duplicate initialization)
• Distance never becomes negative (clamps to 0 if needed)
• Elephant.move(...) delegates to Tracker.move(...)
• Elephant.isInsidePark() delegates to Tracker.isInsidePark()
• toString() output matches the strict formats exactly

Submission

Grading (18 points total)

The project is graded for correctness and adherence to the written specification. A high-level breakdown:

• Compilation and required interfaces
• Correct default values and constructor chaining
• Non-negative distance invariant and movement behavior
• Correct inside/outside computation
• Correct delegation between Elephant and Tracker
• Strict toString() formatting