依赖倒置原则（DSP）
<?php// 司机开奔驰，未用依赖倒置原则的写法class Benz{ public function run(){ return " Benz is runing!!!"; }}class Driver{ public function drive(Benz $car){ echo $car -> run(); }}class Client{ public static function doing(){ $driver = new Driver(); $driver -> drive( new Benz() ); }}Client :: doing();// 那么如果司机想开宝马呢？，是不是就要修改Driver了，这就违反了开闭原则了，怎么能只在Client添加代码就让宝马车也会开呢？interface ICar{ //定义一个汽车接口 public function run();}class BMW implements ICar{ public function run(){ return "BMW is runing !!!"; }}class Benz implements ICar{ public function run(){ return "Benz is runing !!!"; }}interface IDriver{ //定义一个司机接口，以防以后有A照，B照，C照的 public function drive(ICar $car);}class Driver implements IDriver{ public function drive(ICar $car){ echo "
" . $car -> run(); }}class Client{ public static function doing(){ $driver = new Driver(); $driver -> drive( new BMW() ); //开宝马 $driver -> drive( new Benz() ); //开奔驰 . . . . }}Client :: doing();?> 这么简单，学会了吧？依赖倒置原则核心一句话：面向接口编程。