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

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

Classes to Implement

• Elephant.java
• Tracker.java

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

Provided Demo File

• ElephantDemo.java

The demo creates a population of elephants, repeatedly moves them, and displays the results. Use it to see your Elephant and Tracker classes working together in a small application.

Basic Project Tester (Self-Check)

• ProjectBTester.java (basic checks for development and debugging)

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

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

You may also run the basic tester to check specific parts of your implementation:

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

Projects will be evaluated for both correctness and adherence to the project specifications.

Your project will be evaluated on:

• Correct implementation of the required classes and methods
• Correct constructor behavior and initialization
• Correct movement and park-boundary behavior
• Proper use of composition and delegation
• Maintaining required class invariants
• Correct toString() formatting
• Following the implementation requirements described in this project