组合模式

<?php
abstract class Lesson{
    private $duration;
    private $costStrategy;

    function __construct( $duration, CostStrategy $strategy)
    {
        $this->duration = $duration;
        $this->costStrategy = $strategy;
    }

    function cost()
    {
        return $this->costStrategy->cost( $this );
    }

    function chargeType()
    {
        return $this->costStrategy->chargeType( $this );
    }

    function getDuration()
    {
        return $this->duration;
    }
}

class Lecture extends Lesson{
    //lecrure 特定的方法
}

class Seminar extends Lesson{
    //seminar 特定的方法
}

abstract class CostStrategy{
    abstract function cost( Lesson $lesson);
    abstract function chargeType();
}

//以下有不同的计费方式


class TimedCostStrategy extends CostStrategy{
　　//计费方式一
    function cost( Lesson $lesson)
    {
        return $lesson->getDuration()*5;
    }

    function chargeType()
    {
        return "hourly rate";
    }
}


class FixedCostStrategy extends CostStrategy{
　　//计费方式二
    function cost( Lesson $lesson)
    {
        return 30;
    }    

    function chargeType()
    {
        return "fixed rate";
    }
}

$lessons[] = new Seminar(4, new TimedCostStrategy() );
$lessons[] = new Lecture(4, new FixedCostStrategy() );
foreach ($lessons as $lesson) {
print " lesson charge {$lesson->cost}";
print " Charge type: {$lesson->chargeType()} ";
}

通过传递不同的CostStrategy对象，来改变Lesson对象的计算费用方式