通过构造函数和普通方法实现依赖注入

//构造函数实现依赖注入

class Boy1
{
   private $girl = null;
   public function __construct(Girl $girl)
   {
       $this->girl = $girl;
   }

   public function getInfo()
   {
       return "我的女朋友".$this->girl->work();
   }
}
//类外实例化Girl;
$girl = new Girl;
$boy1 = new Boy1($girl);
echo $boy1->getInfo();

echo "<hr>";

//普通方法注入
class Boy2
{
   public function buy(Girl $girl)
   {
       return "我的女朋友".$girl->hobby();
   }
}
$girl = new Girl;
$boy2 = new Boy2;
echo $boy2->buy($girl);

在类外部实例化优势 减少类与类之间耦合性