空对象模式

PHP代码：

<?php

abstract class AbstractCustomer{

  protected $name;
  public abstract function isNil();
  public abstract  function getName();
}


class RealCustomer extends AbstractCustomer {


    public function __construct($name)
    {
        $this->name = $name;    
    }

   public function getName() {
      return $this->name;   
   }


   public function isNil() {
      return false;   
   }

}

class NullCustomer extends AbstractCustomer {

    public function getName() {

       return "Not Available in Customer Database";    
    }


   public function isNil() {
      return true;   
   }


}
class CustomerFactory {

    #PHP中final不能修饰变量，但可以是类和方法
    public static  $names = ["Rob", "Joe", "Julie"];   

    public static function  getCustomer($name){
       //foreach更方便，如果说有点学习点地方就是静态变量必须用静态方法调用，self::$value 

        for ($i = 0; $i < count(self::$names); $i++) {
            if (self::$names[$i] == $name){
                return new RealCustomer($name);            
             }
        }
          return new NullCustomer();       
   }
}

class NullPatternDemo {
    public static function main() {

     $customer1 = CustomerFactory::getCustomer("Rob");     
     $customer2 = CustomerFactory::getCustomer("Bob");     
     $customer3 = CustomerFactory::getCustomer("Julie");     
     $customer4 = CustomerFactory::getCustomer("Laura");     
     echo "Customers".PHP_EOL;     
     echo $customer1->getName().PHP_EOL;     
     echo $customer2->getName().PHP_EOL;     
     echo $customer3->getName().PHP_EOL;     
     echo $customer4->getName().PHP_EOL;    
    }
}

NullPatternDemo::main();

/* *  执行程序，输出结果：    
localhost:bin fangliang$ php /Users/fangliang/Downloads/test.php   
 Customers    Rob    
 Not Available in Customer Database    
 Julie    
 Not Available in Customer Database 

* * */