PHP中类的延迟绑定

<?php
	header("content-type:text/html;charset=utf-8");
	class a{
		public function call(){
			echo "父类的".__CLASS__;
		}
		public static function say(){
			self::call();//直接在父类中调用call方法
		}
		public static function say1(){
			static:: call();//延迟绑定到b的call方法
		}

	}
	class b extends a{
		public function call(){
			echo "子类的".__CLASS__;
		}
	}

	b::say();//父类的a
	b::say1();//子类的b