状态模式的另一种写法

<?php
/**
 * 状态模式
 * 允许一个对象在其内部状态改变时改变它的行为,对象看起来似乎修改了它所属的类
 */

/*接口*/
interface State
{
    public function handle($state);//切换到下一个状态
    public function display();//显示当前状态
}

/*状态A*/
class StateA implements State
{
    public function handle($context)
    {
        $context->setState(new StateB());
    }

    public function display()
    {
        echo "state A<br />";
    }
}
/*状态B*/
class StateB implements State
{
    public function handle($context)
    {
        $context->setState(new StateC());
    }

    public function display()
    {
        echo "state B<br/>";
    }
}
/*状态C*/
class StateC implements State
{
    public function handle($context)
    {
        $context->setState(new StateA());
    }

    public function display()
    {
        echo "state C<br/>";
    }
}


class Context
{
    private $_state = null;
    public function __construct($state)//给初始状态
    {
        $this->setState($state);
    }

    public function setState($state)//设置状态的函数
    {
        $this->_state = $state;
    }

    public function request()//执行显示状态并切换状态
    {
        $this->_state->display();
        $this->_state->handle($this);
    }
}

// 实例化一下
$objContext = new Context(new StateB());
$objContext->request();
$objContext->request();
$objContext->request();
$objContext->request();
$objContext->request();
?>