本文实例讲述了PHP面向对象程序设计高级特性。分享给大家供大家参考,具体如下:
静态属性
<?phpclass 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();?>
输出:0 hello
点评:静态属性和方法,可以通过类直接调用。
SELF
<?phpclass 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();?>
输出:
hello (1)hello (2)hello (3)
点评:self 指向当前类, this指向当前对象。self可以调用当前类的静态属性和方法。this指向当前对象。self可以调用当前类的静态属性和方法。this可以调用当前类的正常属性和方法。
常量属性
<?phpclass ShopProduct { const AVAILABLE = 0; // 只能用大写字母命名常量 const OUT_OF_STOCK = 1; public $status;}print ShopProduct::AVAILABLE;?>
输出:0
点评:常量只能用大写字母,并且可以通过类直接调用。
接口
<?phpinterface 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();?>
如果没有实现getPrice方法,将会报错。
Fatal error: Class ShopProduct contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (Chargeable::getPrice)
继承类与接口
<?phpclass TimedService{ }interface Bookable{ }interface Chargeable{ }class Consultancy extends TimedService implements Bookable, Chargeable { // 继承类与接口 // ...}?>
抽象类
先来看一段代码
<?phpabstract 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 );?>
输出:
Document Object()
静态方法
<?phpabstract class DomainObject { private $group; // 私有属性group public function __construct() { $this->group = static::getGroup();//static 静态类 } public static function create() { return new static(); } static function getGroup() { // 静态方法 return "default"; }}class User extends DomainObject {}class Document extends DomainObject { static function getGroup() { // 改变了内容 return "document"; }}class SpreadSheet extends Document { // 继承之后,group也就与document相同了}print_r(User::create());print_r(SpreadSheet::create());?>
输出:
User Object( [group:DomainObject:private] => default)SpreadSheet Object( [group:DomainObject:private] => document)
final字段
使类无法被继承,用的不多
<?phpfinal class Checkout { // 终止类的继承 // ...}class IllegalCheckout extends Checkout { // ...}$checkout = new Checkout();?>
输出:
Fatal error: Class IllegalCheckout may not inherit from final class (Checkout)
final方法不能够被重写
<?phpclass 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();?>
输出:
Fatal error: Cannot override final method Checkout::totalize()
析构函数
<?phpclass 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( '' ); // 最后执行析构函数,使用完之后执行?>
输出:
do nothing
__clone方法
克隆的时候执行
<?phpclass 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 );?>
输出:
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)
再看一个例子
<?phpclass 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 tooprint $person2->account->balance; // person的属性account也是一个类,他的属性balance的值是210// output:// 210?>
点评:学习还是能够开拓大脑的,今天终于明白为什么有多个箭头的概念了$person->account->balance。这里的account属性是一个对象。
__toString
<?phpclass 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)?>
点评:必须是print或echo时才有效,print_r就输出对象。
Person Object()
希望本文所述对大家PHP程序设计有所帮助。
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