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PHP5中虛函數(shù)的實(shí)現(xiàn)方法分享

更新時(shí)間：2011年04月20日 23:30:49 作者：

學(xué)過(guò)C++的人都應(yīng)該知道C++中有個(gè)虛函數(shù)的概念。而在php5中如何實(shí)現(xiàn)這個(gè)虛函數(shù)呢？

請(qǐng)看下面的代碼：

 
<?php 
class A { 
public function x() { 
echo "A::x() was called.\n"; 
} 
public function y() { 
self::x(); 
echo "A::y() was called.\n"; 
} 
public function z() { 
$this->x(); 
echo "A::z() was called.\n"; 
} 
} 
class B extends A { 
public function x() { 
echo "B::x() was called.\n"; 
} 
} 
$b = new B(); 
$b->y(); 
echo "--\n"; 
$b->z(); 
?> 

該例中，A::y()調(diào)用了A::x()，而B(niǎo)::x()覆蓋了A::x()，那么當(dāng)調(diào)用B::y()時(shí)，B::y()應(yīng)該調(diào)用A::x()還是 B::x()呢？在C++中，如果A::x()未被定義為虛函數(shù)，那么B::y()（也就是A::y()）將調(diào)用A::x()，而如果A::x()使用 virtual關(guān)鍵字定義成虛函數(shù)，那么B::y()將調(diào)用B::x()。然而，在PHP5中，虛函數(shù)的功能是由 self 和 $this 關(guān)鍵字實(shí)現(xiàn)的。如果父類中A::y()中使用 self::x() 的方式調(diào)用了 A::x()，那么在子類中不論A::x()是否被覆蓋，A::y()調(diào)用的都是A::x()；而如果父類中A::y()使用 $this->x() 的方式調(diào)用了 A::x()，那么如果在子類中A::x()被B::x()覆蓋，A::y()將會(huì)調(diào)用B::x()。

上例的運(yùn)行結(jié)果如下：
A::x() was called. A::y() was called. --
B::x() was called. A::z() was called.
virtual-function.php

復(fù)制代碼代碼如下:

 
<?php 
class ParentClass { 
static public function say( $str ) { 
static::do_print( $str ); 
} 
static public function do_print( $str ) { 
echo "<p>Parent says $str</p>"; 
} 
} 
class ChildClass extends ParentClass { 
static public function do_print( $str ) { 
echo "<p>Child says $str</p>"; 
} 
} 
class AnotherChildClass extends ParentClass { 
static public function do_print( $str ) { 
echo "<p>AnotherChild says $str</p>"; 
} 
} 
echo phpversion(); 
$a=new ChildClass(); 
$a->say( 'Hello' ); 
$b=new AnotherChildClass(); 
$b->say( 'Hello' ); 