Bài giảng Phát triển phần mềm nguồn mở - Bài 4: Object Oriented Programming - Nguyễn Hữu Thể

OBJECT ORIENTED PROGRAMMING
Nguyễn Hữu Thể
PHÁT TRIỂN PHẦN MỀM NGUỒN MỞ
Content
1. Class
2. Visibility
3. Properties & Methods
4. Getter & Setter
5. Create objects
6. Constructor
7. Destructor
8. Inheritance
9. Abstract class
10. Interfaces
11. Autoloading classes
12. Anonymous functions
13. Closures
14. Namespace
2
Class 
3
class ClassName
{
// Properties
// Methods
}
Visibility (public, private, protected)
 Three levels:
• public
• private
• protected
 By default, all class members are public.
4
Properties & Methods
5
class Person
{
private $name; //public, protected
private $age;
public function show(){
echo $this->name . " is " . $this->age . " years old!";
}
}
Create objects
(Create a new instance of the class)
 Using the new keyword:
new ClassName()
 For example:
$person = new PerSon();
$person2 = new PerSon();
6
Getter & Setter
7
class Person
{
private $name;
private $age;
public function getName(){
return $this->name;
}
public function setName($name){
$this->name = $name;
}
public function getAge(){
return $this->age;
}
public function setAge($age){
$this->age = $age;
}
}
class Person 
{ 
private String name; 
private int age; 
public String getName(){ 
return name; 
} 
public void setName(String name){ 
this.name = name; 
} 
public int getAge(){ 
return age; 
} 
public void setAge(int age){ 
this.age = age; 
} 
} 
PHP JAVA
8class Person{
private $name;
private $age;
public function getName(){
return $this->name;
}
public function setName($name){
$this->name = $name;
}
public function getAge(){
return $this->age;
}
public function setAge($age){
$this->age = $age;
}
public function show(){
echo $this->name . " is " . $this->age . " years old!";
}
} $p = new Person();
$p->setName("Nguyễn Văn A");
$p->setAge(18);
echo $p->getName() . " is " . $p->getAge() . " years old.";
//echo "{$p->getName()} is {$p->getAge()} years old.";
$p->show();
Ex: Person.php
__set() method
9
class SetName {
public function __set($variable, $value) {
// echo $variable;
echo "My " . $variable . " is " . $value . "\n";
}
}
$obj = new SetName ();
$obj->Name = ‘Tom';
$obj->Name = ‘Jerry';
My Name is Tom
My Name is Jerry
__get() method
10
class GetName {
public $type = 'chocolate';
public $choctype = array (
'milk' => 0,
'dark' => 1,
'plain' => 2 
);
public function wrap() {
echo 'Its a wrap';
}
public function __get($index) {
echo '$choctype property with index of: ' . $index . '';
return $this->choctype [$index];
}
}
$candy = new GetName ();
// set a non existant property
echo 'Value of property is: ' . $candy->milk; $choctype property with index of: milk
Value of property is: 0
Constructor
11
public function __construct($name, $age) {
//...
}
public function __construct() {
//...
}
Constructor
12
class Person{
private $name;
private $age;
public function __construct($name, $age) {
$this->name = $name;
$this->age = $age;
}
public function show(){
echo $this->name . " is " . $this->age . " years old!";
}
}
$p = new Person("Nguyễn Trần Lê", 18);
$p->show();
Destructor
 Example:
 Using: 
13
public function __destruct() {
//...
}
public function __destruct() {
echo "Bye bye!";
//...
}
$p = new Person("Nguyễn Trần Lê", 18);
unset( $p ); // or exit: call __destruct() object
$p->show(); // Object not found
Inheritance
14
class ParentClass {
public function myMethod() {
// Method code here
}
}
class ChildClass extends ParentClass {
public function myMethod() {
// For ChildClass objects, this method is called
// instead of the parent class's MyMethod()
}
}
Calling a parent method from a child method
15
parent::myMethod();
parent::show();
parent::__construct();
Example:
Inheritance
16
require_once 'Person.php';
class Employee extends Person{
private $salary;
public function __construct($name, $age, $salary){
parent::__construct($name, $age); // Call __construct() parent
$this->salary = $salary;
}
public function getSalary(){
return $salary;
}
// Override
public function show(){
parent::show();
echo " Salary: " . $this->salary;
}
public function display(){
echo " Name: " . $this->getName() . "";
echo " Age: " . $this->getAge() . "";
echo "Salary: " . $this->salary;
}
}
$e = new Employee("Nguyễn Lê", 20, 200);
$e->show();
Nguyễn Lê is 20 years old! Salary: 200
Visibility (Example 1)
Property Visibility
17
class MyClass {
public $public = 'Public';
protected $protected = 'Protected';
private $private = 'Private';
function printHello() {
echo $this->public;
echo $this->protected;
echo $this->private;
}
}
$obj = new MyClass();
echo $obj->public; // Works
echo $obj->protected; // Fatal Error
echo $obj->private; // Fatal Error
$obj->printHello(); // Shows Public, Protected and Private
Visibility (Example 2)
Property Visibility
18
class MyClass2 extends MyClass {
// We can redeclare the public and protected method, but not private
public $public = 'Public2';
protected $protected = 'Protected2';
function printHello() {
echo $this->public;
echo $this->protected;
echo $this->private;
}
}
$obj2 = new MyClass2();
echo $obj2->public; // Works
echo $obj2->protected; // Fatal Error
echo $obj2->private; // Undefined
$obj2->printHello(); // Shows Public2, Protected2, Undefined
Visibility (Example 3)
Method Visibility
19
class MyClass {
// Declare a public constructor
public function __construct() { }
// Declare a public method
public function MyPublic() { }
// Declare a protected method
protected function MyProtected() { }
// Declare a private method
private function MyPrivate() { }
// This is public
function Foo() {
$this->MyPublic();
$this->MyProtected();
$this->MyPrivate();
}
}
$myclass = new MyClass;
$myclass->MyPublic(); // Works
$myclass->MyProtected(); // Fatal Error
$myclass->MyPrivate(); // Fatal Error
$myclass->Foo(); // Public, Protected and Private work
Visibility (Example 4)
Method Visibility
20
class MyClass2 extends MyClass
{
// This is public
function Foo2()
{
$this->MyPublic();
$this->MyProtected();
$this->MyPrivate(); // Fatal Error
}
}
$myclass2 = new MyClass2;
$myclass2->MyPublic(); // Works
$myclass2->Foo2(); // Public and Protected work, not Private
Visibility (Example 5)
Method Visibility
21
class Bar
{
public function test() {
$this->testPrivate();
$this->testPublic();
}
public function testPublic() {
echo "Bar::testPublic\n";
}
private function testPrivate() {
echo "Bar::testPrivate\n";
}
}
class Foo extends Bar
{
public function testPublic() {
echo "Foo::testPublic\n";
}
private function testPrivate() {
echo "Foo::testPrivate\n";
}
}
$myFoo = new Foo();
$myFoo->test(); // Bar::testPrivate
// Foo::testPublic
Abstract class
 An abstract class is a class that cannot be instantiated on its 
own.
22
abstract class Mathematics{
/*** child class must define these methods ***/
abstract protected function getMessage();
abstract protected function add($num);
/**
* method common to both classes
**/
public function showMessage() {
echo $this->getMessage();
}
}
Abstract class
23
require_once 'Mathematics.php';
class myMath extends Mathematics {
protected function getMessage() {
return "The anwser is: ";
}
public function add($num) {
return $num + 2;
}
}
// A new instance of myMath
$myMath = new MyMath ();
$myMath->showMessage ();
echo $myMath->add (4);
The anwser is: 6
Interfaces
 An interface declares one or more methods.
 Must be implemented by any class that implements the 
interface.
24
interface MyInterface {
public function aMethod();
public function anotherMethod();
}
class MyClass implements MyInterface {
public function aMethod() {
// (code to implement the method)
}
public function anotherMethod() {
// (code to implement the method)
}
}
interface Persistable {
public function save();
public function load();
public function delete();
}
require_once 'Persistable.php';
class Member implements Persistable {
private $username;
private $location;
private $homepage;
public function __construct( $username, 
$location, $homepage ) {
$this->username = $username;
$this->location = $location;
$this->homepage = $homepage;
}
public function getUsername() {
return $this->username;
}
public function getLocation() {
return $this->location;
}
public function getHomepage() {
return $this->homepage;
}
public function save() {
echo "Saving member to 
database";
}
public function load() {
echo "Loading member from 
database";
}
public function delete () {
echo "Deleting member from 
database";
}
}
$m = new Member("Aha", "VN", "No page");
echo $m->getUsername() . "";
$m->load();
//...
Aha
Loading member from database
class Topic implements Persistable {
private $subject;
private $author;
private $createdTime;
public function __construct( $subject, $author ) {
$this->subject = $subject;
$this->author = $author;
$this->createdTime = time();
}
public function showHeader() {
$createdTimeString = date( 'l jS M Y h:i:s A', $this->createdTime );
$authorName = $this->author->getUsername();
echo "$this->subject (created on $createdTimeString by $authorName)";
}
public function save() {
echo "Saving topic to database";
}
public function load() {
echo "Loading topic from database";
}
public function delete () {
echo "Deleting topic from database";
}
}
require_once 'Member.php';
require_once 'Topic.php';
$aMember = new Member ( "TUI", "Viet Nam", "" );
echo $aMember->getUsername () . " lives in " . $aMember->getLocation () . "";
$aMember->save ();
$aTopic = new Topic ( "PHP is Great", $aMember );
$aTopic->showHeader ();
$aTopic->save ();
TUI lives in Viet Nam
Saving member to database
PHP is Great (created on Saturday 17th Dec 2016 03:00:07 AM by TUI)
Saving topic to database
Test.php
Autoloading classes
 Create a function called __autoload() near the start of
your PHP application.
 PHP automatically calls your __autoload() function.
28
function __autoload($className) {
require_once ("$className.php");
echo "Loaded $className.php";
}
$member = new Member("TUI", "Viet Nam", "No page");
echo "Created object: ";
print_r ( $member );
Loaded Member.php
Created object: Member Object ( [username:Member:private] => TUI 
[location:Member:private] => Viet Nam [homepage:Member:private] => No page ) 
Anonymous functions
 Anonymous functions have no name. 
29
// Assign an anonymous function to a variable
$makeGreeting = function ($name, $timeOfDay) {
return ('Good ' . $timeOfDay . ', ' . $name);
};
// Call the anonymous function
echo $makeGreeting ( 'Tom', 'morning' ) . '';
echo $makeGreeting ( 'Jerry', 'afternoon' ) . '';
Good morning, Tom
Good afternoon, Jerry
Closures
 A closure is an anonymous function that can access variables 
imported from the outside scope without using any global 
variables.
30
function myClosure($num) {
return function ($x) use ($num) {
return $num * $x;
};
}
$closure = myClosure ( 10 );
echo $closure ( 2 );
echo $closure ( 3 );
20
30
Namespaces
 Namespaced code is defined using a singlenamespace 
keyword at the top of your PHP file. 
 It must be the first command (with the exception ofdeclare) 
and no non-PHP code, HTML, or white-space
31
// define this code in the 'MyProject' namespace
namespace MyProject;
// ... code ...
namespace foo;
class Cat {
static function says() {
echo 'Meoow';
}
}
namespace bar;
class Dog {
static function says() {
echo 'Ruff';
}
}
namespace other\animate;
class Animal {
static function breathes() {
echo 'Air';
}
}
namespace test;
include 'Cat.php';
include 'Dog.php';
include 'Animal.php';
use foo as cat;
use bar as dog;
//use other\animate;
use other\animate as animal;
echo cat\Cat::says (), "";
echo dog\Dog::says (), "";
echo animal\Animal::breathes ();
//echo \other\animate\Animal::breathes ();
Cat.php
Dog.php
Animal.php
Test.php
Result:
Meoow
Ruff
Air