PHP Simple OOP Example - Graduate and Undergraduate Students

students.php

<?php

class Student
{
	protected $name;
	/** 
	 * social security number
	 * @var string **/
	protected $ssn;
	protected $major;
	protected $gpa;
	
	function __construct($name, $ssn, $major=null) {
		$this->name = $name;
		$this->ssn = $ssn;
		$this->major = $major;
	}
	
	function getName() {
		return $this->name;
	}
	
	function changeName($newName) {
		$this->name = $newName;
	}
	
	function getSsn() {
		return $this->ssn;
	}
	
	function getMajor() {
		if ($this->major == null) {
			return 'Undeclared';
		}
		return $this->major;
	}
	
	function changeMajor($newMajor) {
		$this->major = $newMajor;
	}
	
	function getGPA() {
		//Throwing an exception here is optional; it depends on the application.
		//We could alternatively consider it the programmer's responsibility to make sure
		//the GPA is set before attempting to retrieve it (or test for null).
		if ($this->gpa == null) {
			throw new Exception("GPA was not set");
		}
		return $this->gpa;
	}
	
	function setGPA($newGpa) {
		$this->gpa = $newGpa;
	}
}

class GraduateStudent extends Student
{
	const MASTERS = 1;
	const PHD = 2;

	private $degreeType;
	
	function __construct($name, $ssn, $degreeType, $major=null) {
		parent::__construct($name, $ssn, $major);
		$this->setDegreeType($degreeType);
	}
	
	function getDegreeType() {
		return $this->degreeType;
	}
	
	function setDegreeType($degree) {
		if ($degree != self::MASTERS && $degree != self::PHD) {
			throw new InvalidArgumentException("Degree must be a constant for either Masters or PhD");
		}	
		$this->degreeType = $degree;
	}
}

class UndergraduateStudent extends Student
{
	private $whichYear;
	private static $validYears = array(
		'freshman',
		'sophomore',
		'junior',
		'senior'
	);
	
	function __construct($name, $ssn, $whichYear, $major=null) {
		parent::__construct($name, $ssn, $major);
		$this->setYear($whichYear);
	}
	
	function getYear() {
		return $this->whichYear;
	}
	
	function setYear($year) {
		if (!in_array($year, self::$validYears)) {
			throw new InvalidArgumentException("Invalid year '$year'");
		}
		$this->whichYear = $year;
	}
}

$fred = new GraduateStudent('Fred', '456-78-9012', GraduateStudent::MASTERS, 'Art');
$fred->setGPA('3.7');

$alice = new UndergraduateStudent('Alice', '123-45-6789', 'freshman');
$alice->setGPA('4.0');

echo "Fred's GPA is ". number_format($fred->getGPA(), 2)."\n";
if ($fred->getDegreeType() == GraduateStudent::MASTERS) {
	echo "Fred is pursuing a Masters in ".$fred->getMajor()."\n";
}

echo "Alice's GPA is ". $alice->getGPA()."\n";
echo "Alice's major is ". $alice->getMajor()."\n";
echo "Alice was a ".$alice->getYear();
$alice->setYear('sophomore');
echo " but is now a ".$alice->getYear()."\n";



class School
{
	protected $name;
	protected $students = array();
	
	public function __construct($name) {
		$this->name = $name;
	}
	
	public function changeName($newName) {
		$this->name = $newName;
	}
	
	public function addStudent(Student $student) {
		$this->students[$student->getSsn()] = $student;
	}
	
	public function getStudent($ssn) {
		if (!isset($this->students[$ssn])) {
			throw new Exception("Student with SSN '$ssn' not found in school '$this->name'!");
		}
		return $this->students[$ssn];
	}
	
	public function graduate(Student $student) {
		$this->issueDiploma($student);
		$this->removeStudent($student);
	}
	
	public function kickOut(Student $student) {
		echo "Be gone with you!";
		$this->removeStudent($student);
	}
	
	protected function issueDiploma(Student $student) {
		echo "Yay, ".$student->getName()." gets a diploma!";
	}
	
	protected function removeStudent(Student $student) {
		unset($this->students[$student->getSsn()]);
	}
}

$RISD = new School('Rhode Island School of Design');
$RISD->addStudent($fred);
$fredsSSN = $fred->getSsn();
unset($fred);

//Later...

$fred = $RISD->getStudent($fredsSSN);
$RISD->graduate($fred);