Head First-策略模式，headfirst-策略

<?php
abstract class Duck{
    public $flyBehavior;
    public $quackBehavior;    

    public function __construct(){
    }

    public function performFly(){
        $this->flyBehavior->fly();
    }

    public function performQuack(){
        $this->quackBehavior->quack();
    }

    public function setFlyBehavior(FlyBehavior $fb){
        $this->flyBehavior = $fb;
    }

    public function setQuackBehavior(QuackBehavior $qb){
        $this->quackBehavior = $qb;
    }

    public function swim(){

    }
    
    abstract function display();
}

interface FlyBehavior{
    public function fly();
}
class FlywithWings implements FlyBehavior{
    public function fly(){
        echo "i'm flying!\n";
    }
}
class FlyNoWay implements FlyBehavior{
    public function fly(){
        echo "i can't fly.\n";
    }
}
class FlyRocketPowered implements FlyBehavior{
    public function fly(){
        echo "i'm flying with a rocket!\n";
    }
}

interface QuackBehavior{
    public function quack();
}
class Quack implements QuackBehavior{
    public function quack(){
        echo "quack!\n";
    }
}
class MuteQuack implements QuackBehavior{
    public function quack(){
        echo "silence\n";
    }
}


class MallardDuck extends Duck{
    public function __construct(){
        $this->quackBehavior = new Quack();
        $this->flyBehavior = new FlyNoWay();
    }

    public function display(){
        echo "i'm a real mallar duck\n";
    }    
}

$duck = new MallardDuck;
$duck->performFly();
$duck->setFlyBehavior(new FlyRocketPowered);
$duck->performFly();
?>