php类

<?php
class A
{
	function f1()
	{
		if(isset($this)){
			echo "is defined,".get_class($this)."\n";
		}else{
			echo "is not defined\n";
		}
	}
}

class B
{
	function f2()
	{
		A::f1();
	}
}

$a = new A;
$b = new B;
$a->f1();
A::f1();
$b->f2();
B::f2();

?> 

is defined,A
is not defined
is defined,B
is not defined

<?php

class A
{
	function f1()
	{
		echo "a1\n";
	}
	function f2()
	{
		echo "a2\n";
	}
}

class B extends A 
{
    function f1()
    {
    	echo "b1\n";
    }
}

$a = new A();
$a->f1();
$b = new B();
$b->f1();
$b->f2();
?> 

a1
b1
a2