Detailed explanation of advanced features of PHP object-oriented programming (interface, inheritance, abstract class, destruction, cloning, etc.)

The examples in this article describe the advanced features of PHP object-oriented programming. Share it with everyone for your reference, the details are as follows:

static properties

<?php
class StaticExample {
  static public $aNum = 0; // 静态共有属性
  static public function sayHello() { // 静态共有方法
    print "hello";
  }
}
print StaticExample::$aNum;
StaticExample::sayHello();
?>

Output: 0 hello

Comments: Static properties and methods can be called directly through classes.

SELF

<?php
class StaticExample {
  static public $aNum = 0;
  static public function sayHello() { // 这里的static 和 public的顺序可以颠倒
    self::$aNum++;
    print "hello (".self::$aNum.")\n"; // self 指向当前类, $this指向当前对象。
  }
}
StaticExample::sayHello();
StaticExample::sayHello();
StaticExample::sayHello();
?>

Output:

hello (1)
hello (2)
hello (3)

Comments: self points to the current class, this points to the current object. self can call static properties and methods of the current class. this points to the current object. self can call static properties and methods of the current class. this can call the normal properties and methods of the current class.

Constant attribute

<?php
interface Chargeable { // 接口,抽象类是介于基类与接口之间的东西
  public function getPrice();
}
class ShopProduct implements Chargeable {
  // ...
  protected $price;
  // ...
  public function getPrice() {
    return $this->price;
  }
  // ...
}
$product = new ShopProduct();
?>

If the getPrice method is not implemented, an error will be reported.

Fatal error: Class ShopProduct contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (Chargeable::getPrice)

Inherited classes and interfaces

<?php
class TimedService{ }
interface Bookable{ }
interface Chargeable{ }
class Consultancy extends TimedService implements Bookable, Chargeable { // 继承类与接口
  // ...
}
?>

Abstract Class

Let’s look at a piece of code first

<?php
abstract class DomainObject {
}
class User extends DomainObject {
  public static function create() {
    return new User();
  }
}
class Document extends DomainObject {
  public static function create() {
    return new Document();
  }
}
$document = Document::create();
print_r( $document );
?>

Output:

Document Object
(
)

Static method

<?php
abstract class DomainObject {
  private $group; // 私有属性group
  public function __construct() {
    $this->group = static::getGroup();//static 静态类
  }
  public static function create() {
    return new static();
  }
  static function getGroup() { // 静态方法
    return "default";
  }
}
class User extends DomainObject {
}
class Document extends DomainObject {
  static function getGroup() { // 改变了内容
    return "document";
  }
}
class SpreadSheet extends Document { // 继承之后，group也就与document相同了
}
print_r(User::create());
print_r(SpreadSheet::create());
?>

Output :

User Object
(
  [group:DomainObject:private] => default
)
SpreadSheet Object
(
  [group:DomainObject:private] => document
)

final field

Makes the class unable to be inherited, not used much

<?php
final class Checkout { // 终止类的继承
  // ...
}
class IllegalCheckout extends Checkout {
  // ...
}
$checkout = new Checkout();
?>

Output:

Fatal error: Class IllegalCheckout may not inherit from final class (Checkout)

The final method cannot be overridden

<?php
class Checkout {
  final function totalize() {
    // calculate bill
  }
}
class IllegalCheckout extends Checkout {
  function totalize() { // 不能重写final方法
    // change bill calculation
  }
}
$checkout = new Checkout();
?>

Output:

Fatal error: Cannot override final method Checkout::totalize()

Destructor

<?php
class Person {
  protected $name;
  private $age;
  private $id;
  function __construct( $name, $age ) {
    $this->name = $name;
    $this->age = $age;
  }
  function setId( $id ) {
    $this->id = $id;
  }
  function __destruct() { // 析构函数
    if ( ! empty( $this->id ) ) {
      // save Person data
      print "saving person\n";
    }
    if ( empty( $this->id ) ) {
      // save Person data
      print "do nothing\n";
    }
  }
}
$person = new Person( "bob", 44 );
$person->setId( 343 );
$person->setId( &#39;&#39; ); // 最后执行析构函数，使用完之后执行
?>

Output:

do nothing

__clone method

Executed when cloning

<?php
class Person {
  private $name;
  private $age;
  private $id;
  function __construct( $name, $age ) {
    $this->name = $name;
    $this->age = $age;
  }
  function setId( $id ) {
    $this->id = $id;
  }
  function __clone() { // 克隆时候执行
    $this->id = 0;
  }
}
$person = new Person( "bob", 44 );
$person->setId( 343 );
$person2 = clone $person;
print_r( $person );
print_r( $person2 );
?>

Output:

Person Object
(
  [name:Person:private] => bob
  [age:Person:private] => 44
  [id:Person:private] => 343
)
Person Object
(
  [name:Person:private] => bob
  [age:Person:private] => 44
  [id:Person:private] => 0
)

Look at another example

<?php
class Account { // 账户类
  public $balance; // 余额
  function __construct( $balance ) {
    $this->balance = $balance;
  }
}
class Person {
  private $name;
  private $age;
  private $id;
  public $account;
  function __construct( $name, $age, Account $account ) {
    $this->name = $name;
    $this->age = $age;
    $this->account = $account;
  }
  function setId( $id ) {
    $this->id = $id;
  }
  function __clone() {
    $this->id  = 0;
  }
}
$person = new Person( "bob", 44, new Account( 200 ) ); // 以类对象作为参数
$person->setId( 343 );
$person2 = clone $person;
// give $person some money
$person->account->balance += 10;
// $person2 sees the credit too
print $person2->account->balance; // person的属性account也是一个类，他的属性balance的值是210
// output:
// 210
?>

Comment: Learning can still open up the brain. Today I finally understand why there are multiple arrow concepts $person->account->balance. The account attribute here is an object.

__toString

<?php
class Person {
  function getName() { return "Bob"; }
  function getAge() { return 44; }
  function __toString() {
    $desc = $this->getName()." (age ";
    $desc .= $this->getAge().")";
    return $desc;
  }
}
$person = new Person();
print $person; // 打印时候集中处理
// Bob (age 44)
?>

Comments: It must be valid only if it is print or echo, print_r will output the object.

Person Object()

I hope this article will be helpful to everyone in PHP programming.

For more detailed explanations of advanced features of PHP object-oriented programming (interfaces, inheritance, abstract classes, destruction, cloning, etc.), please pay attention to the PHP Chinese website!