单一模式 与 工厂模式 例题

设计模式
1.单例模式
类的计划生育
1.让该类在外界无法造对象
2.让外界可以造一个对象，做一个静态方法返回对象
3.在类里面通过静态变量控制返回对象只能是一个

<?php
class Dog
{
static $dx;
public $test;
private function __construct()
{

}
static function duixiang()
{
if(empty(self::$dx))
{
self::$dx=new Dog();
}
return self::$dx;
}

}
$a=Dog::duixiang();
$b=Dog::duixiang();
$b->test="素质教育";
var_dump($b);

class Yunsuan
{
public $a;
public $b;

function jia()
{
return $this->a+$this->b;
}
function jian()
{
return $this->a+ $this->b;
}

}
$r=new Yunsuan();
$r->a=10;
$r->b=5;
echo $r->jian();

abstract class yunsuan //抽象类
{ public $a;
public $b;

function suan()
{
}

}

class jia extends yunsuan
{
function suan()
{
return $this->a+$this->b;

}
}

class jian extends yunsuan
{
function suan    ()
{
return $this->a-$this->b;
}

}

class cheng extends yunsuan
{
function suan()
{
return $this->a*$this->b;

}
}

/*$j= new jia();

$j->a=10;

$j->b=7;

echo $j->suan();
*/
class Gongchang
{
static function shengchan($f)
{
switch ($f)
{
case"+":return new jia();break;
case"-":return new jian();break;
case"*":return new cheng();break; 

}
}
}

$r=gongchang::shengchan("*");
$r->a=99999;
$r->b=34567;
echo $r->suan();