php 的继承中需要注意的地方

php的继承功能还很不完善，并且很容易出错。运行下面的代码，看看结果是否是你所要的。

<?php
	interface IA
	{
		public function Print1();
		public function Print2();
		//private function Pritn3(); //error
		//public $m_var1; //error
	};
	abstract class CB
	{
		public abstract function Echo1();
		//private abstract function Echo2(); //error
		
		public function Echo3()
		{
			echo "CB::Echo3<br>";
			echo "m_var1 = " . $this->m_var1 . "<br>";
			echo "m_var2 = " . $this->m_var2 . "<br>";
			echo "m_var3 = " . $this->m_var3 . "<br>";
			echo "m_var4 = " . $this->m_var4 . "<br>";
			echo "m_var = " . CB::m_var . "<br>";
			echo "static m_var3 = " . CB::$m_var3 . "<br>";
		
		}
		public $m_var1;
		private $m_var2;
		public static $m_var3 = 11;
		protected $m_var4;
		const m_var = 10; //声明为常量
	};
	class CC implements IA
	{
		public function CC()
		{
			echo "constructor of CC has been called!<br>";
		}
		public function __destructor()
		{
			echo "destructor of CC has been called!<br>";
		}
		function Print1()
		{
			echo "CC::Print1()<br>";
		}
		function Print2()
		{
			echo "CC::Print2()<br>";
		}
	};
	class CD extends CB
	{
		public function CD()
		{
			echo "constructor of CD has been called!<br>";
			//parent::$m_var1 = 1; //error
			$this->m_var1 = 1;
			$this->m_var2 = 2;	//因为父类中位private所以，无法直接去访问。因此，隐式的定义了一个变量		
			$this->m_var3 = 3;
			$this->m_var4 = 4;
			$this->m_var = 5;
		}
		function Echo1()
		{
			echo "CD::Echo1()<br>";
		}
	};
?>
<?php
	//$objA = new IA;
	//$objB = new CB;
	$objC = new CC;
	$objD = new CD;
	$objC->Print1();
	$objC->Print2();
	$objD->Echo1();
	$objD->Echo3();
?>

结果：

constructor of CC has been called!
constructor of CD has been called!
CC::Print1()
CC::Print2()
CD::Echo1()
CB::Echo3
m_var1 = 1
m_var2 =
m_var3 = 3
m_var4 = 4
m_var = 10
static m_var3 = 11