PHP面向对象深入研究之【高级特性】
静态属性
<?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();
?>
输出：0 hello
点评：静态属性和方法，可以通过类直接调用。
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();
?>
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可以调用当前类的正常属性和方法。
常量属性
<?php
class 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
<?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();
?>
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
<?php
class 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
<?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 );
?>
输出：
Document Object
(
)
静态方法
<?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());
?>
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
<?php
final 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
<?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();
?>
输出：
Fatal error: Cannot override final method Checkout::totalize()
析构函数
<?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( '' ); // 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
<?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 );
?>
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
<?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 $person2->account->balance; // person的属性account也是一个类，他的属性balance的值是210
// output:
// 210
?>
点评：学习还是能够开拓大脑的，今天终于明白为什么有多个箭头的概念了$person->account->balance。这里的account属性是一个对象。
__toString
<?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)
?>
点评：必须是print或echo时才有效，print_r就输出对象。
Person Object()
