PHP5中虚函数的实现方法分享
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2023-11-09 22:45:16
请看下面的代码： 复制代码 代码如下:
请看下面的代码：
<?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();
?>
该例中，a::y()调用了a::x()，而b::x()覆盖了a::x()，那么当调用b::y()时，b::y()应该调用a::x()还是 b::x()呢？在c++中，如果a::x()未被定义为虚函数，那么b::y()（也就是a::y()）将调用a::x()，而如果a::x()使用 virtual关键字定义成虚函数，那么b::y()将调用b::x()。然而，在php5中，虚函数的功能是由 self 和 $this 关键字实现的。如果父类中a::y()中使用 self::x() 的方式调用了 a::x()，那么在子类中不论a::x()是否被覆盖，a::y()调用的都是a::x()；而如果父类中a::y()使用 $this->x() 的方式调用了 a::x()，那么如果在子类中a::x()被b::x()覆盖，a::y()将会调用b::x()。
上例的运行结果如下：
a::x() was called. a::y() was called. --
b::x() was called. a::z() was called.
virtual-function.php
<?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' );
复制代码 代码如下:
<?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();
?>
该例中，a::y()调用了a::x()，而b::x()覆盖了a::x()，那么当调用b::y()时，b::y()应该调用a::x()还是 b::x()呢？在c++中，如果a::x()未被定义为虚函数，那么b::y()（也就是a::y()）将调用a::x()，而如果a::x()使用 virtual关键字定义成虚函数，那么b::y()将调用b::x()。然而，在php5中，虚函数的功能是由 self 和 $this 关键字实现的。如果父类中a::y()中使用 self::x() 的方式调用了 a::x()，那么在子类中不论a::x()是否被覆盖，a::y()调用的都是a::x()；而如果父类中a::y()使用 $this->x() 的方式调用了 a::x()，那么如果在子类中a::x()被b::x()覆盖，a::y()将会调用b::x()。
上例的运行结果如下：
a::x() was called. a::y() was called. --
b::x() was called. a::z() was called.
virtual-function.php
复制代码 代码如下:
<?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' );