php面向对象要点[转]

• __construct

<?phpclass ConstructTest {    private $arg1;    private $arg2;    public function __construct($arg1, $arg2) {        $this->arg1 = $arg1;        $this->arg2 = $arg2;        print "__construct is called...\n";    }    public function printAttributes() {        print '$arg1 = '.$this->arg1.' $arg2 = '.$this->arg2."\n";    }}$testObject = new ConstructTest("arg1","arg2"); $testObject->printAttributes();

运行结果如下：

Stephens-Air:Desktop$ php Test.php __construct is called...$arg1 = arg1 $arg2 = arg2

• parent

用于在子类中直接调用父类中的方法

<?phpclass BaseClass {    protected $arg1;    protected $arg2;    function __construct($arg1, $arg2) {        $this->arg1 = $arg1;        $this->arg2 = $arg2;        print "__construct is called...\n";    }    function getAttributes() {        return '$arg1 = '.$this->arg1.' $arg2 = '.$this->arg2;    }}class SubClass extends BaseClass {    protected $arg3;    function __construct($baseArg1, $baseArg2, $subArg3) {        parent::__construct($baseArg1, $baseArg2);        $this->arg3 = $subArg3;    }    function getAttributes() {        return parent::getAttributes().' $arg3 = '.$this->arg3;    }}$testObject = new SubClass("arg1","arg2","arg3"); print $testObject->getAttributes()."\n";

运行结果如下：

Stephens-Air:Desktop$ php Test.php __construct is called...$arg1 = arg1 $arg2 = arg2 $arg3 = arg3

• self
  在类内调用该类静态成员和静态方法的前缀修饰，对于非静态成员变量和函数则使用this。

<?phpclass StaticExample {    static public $arg1 = "Hello, This is static field.\n";    static public function sayHello() {        print self::$arg1;    }}print StaticExample::$arg1;StaticExample::sayHello();

• static
  这里介绍的static关键字主要用于PHP 5.3以上版本新增的延迟静态绑定功能。

<?phpabstract class Base {    public static function getInstance() {        //这里的new static()实例化的是调用该静态方法的当前类。        return new static();    }    abstract public function printSelf(); }class SubA extends Base {    public function printSelf() {        print "This is SubA::printSelf.\n";    }}class SubB extends Base {    public function printSelf() {        print "This is SubB::printSelf.\n";    }}SubA::getInstance()->printSelf();SubB::getInstance()->printSelf();

运行结果如下：

Stephens-Air:Desktop$ php Test.php This is SubA::printSelf.This is SubB::printSelf.

static关键字不仅仅可以用于实例化。和self和parent一样，static还可以作为静态方法调用的标识符，甚至是从非静态上下文中调用。在该场景下，self仍然表示的是当前方法所在的类。见如下代码：

<?phpabstract class Base {    private $ownedGroup;    public function __construct() {        //这里的static和上面的例子一样，表示当前调用该方法的实际类。        //需要另外说明的是，这里的getGroup方法即便不是静态方法，也会得到相同的结果。然而倘若        //getGroup真的只是普通类方法，那么这里还是建议使用$this。        $this->ownedGroup = static::getGroup();    }    public function printGroup() {        print "My Group is ".$this->ownedGroup."\n";    }    public static function getInstance() {        return new static();    }    public static function getGroup() {        return "default";    }}class SubA extends Base {}class SubB extends Base {    public static function getGroup() {        return "SubB";    }}SubA::getInstance()->printGroup();SubB::getInstance()->printGroup(); 

运行结果如下：

Stephens-Air:Desktop$ php Test.php My Group is defaultMy Group is SubB

• __destruct
  析构方法的作用和构造方法__construct刚好相反，它只是在对象被垃圾收集器收集之前自动调用，我们可以利用该方法做一些必要的清理工作。

<?phpclass TestClass {    function __destruct() {        print "TestClass destructor is called.\n";    }}$testObj = new TestClass();unset($testObj);print "Application will exit.\n";

运行结果如下：

Stephens-Air:Desktop$ php Test.php TestClass destructor is called.Application will exit.

• __clone
  在PHP 5之后的版本中，对象之间的赋值为引用赋值，即赋值后的两个对象将指向同一地址空间，如果想基于对象赋值，可以使用PHP提供的clone方法。该方法将当前对象浅拷贝之后的副本返回，如果想在clone的过程中完成一些特殊的操作，如深拷贝，则需要在当前类的声明中实现__clone方法，该方法在执行clone的过程中会被隐式调用。另外需要格外注意的是，__clone方法是作用再被拷贝的对象上，即赋值后的对象上执行。

<?phpclass InnerClass {    public $id = 10;    public function printSelf() {        print '$id = '.$this->id."\n";    }}class OuterClass {    public $innerClass;    public function __construct() {        $this->innerClass = new InnerClass();    }    public function __clone() {        $this->innerClass = clone $this->innerClass;        print "__clone is called.\n";    }}$outerA = new OuterClass();print "Before calling to clone.\n";$outerB = clone $outerA;print "After calling to clone.\n";$outerA->innerClass->id = 20;print "In outerA: ";$outerA->innerClass->printSelf();print "In outerB: ";$outerB->innerClass->printSelf();

运行结果如下：

Stephens-Air:Desktop$ php Test.php Before calling to clone.__clone is called.After calling to clone.In outerA: $id = 20In outerB: $id = 10

• const
  PHP5可以在类中定义常量属性。和全局常量一样，一旦定义就不能改变。常量属性不需要像普通属性那样以开头，按照惯例，只能用大写字母来命名常量。另外和静态属性一样，只能通过类而不能通过类的实例访问常量属性，引用常量时同样也不需要以符号作为前导符。另外常量只能被赋值为基础类型，如整型，而不能指向任何对象类型。

<?phpclass TestClass {    const AVAILABLE = 0;}print "TestClass::AVAILABLE = ".TestClass::AVAILABLE."\n";

运行结果如下：

0Stephens-Air:Desktop$ php Test.php TestClass::AVAILABLE = 0