php中的parent、self、static关键字

<?phpclass BaseClass{	public function test(){		echo "BaseClass::test called\n";	}	public function test1(){		echo "BaseClass::test1 called\n";	}}class ChildClass extends BaseClass{	const CONST_VALUE = "A constant value\n";	private static $sValue = "static value\n";	public function  test(){		echo "ChildClass::test called\n";		parent::test();		//使用parent关键字可以访问父类中被子类重写的方法		self::called();		echo self::CONST_VALUE;		echo self::$sValue;		//使用self关键字可以访问自身的成员方法和常量成员	}	public function called(){		echo "ChildClass::called() called\n";	}}$obj = new ChildClass();$obj->test();