PHP设计模式之装饰模式

本文知识来源于：《深入PHP面向对象、模式和实践》一书

<?php
/*
Title:装饰模式
Detail:平原、污染、钻石对象的独立和组合。
*/
abstract class Tile{
abstract function getWealthFactor();
}

//平原类，wealthfactor为财富值
class Plains extends Tile{
private $wealthfactor=2;
function getWealthFactor(){
return $this->wealthfactor;
}
}

//含钻石土地类
class DiamondPlains extends Plains{
function getWealthFactor(){
return parent::getWealthFactor()+2;
}
}

//污染土地类
class PollutedPlains extends Plains{
function getWealthFactor(){
return parent::getWealthFactor()-4;
}
}

//以上的类的实现，我们可以轻松获得每个类型的土地的财富价值

问题：

如果出现一个即被污染也含钻石的土地，

要去计算它的财富价值，

那么我们是否应该去创建多一个类呢？

答案：

不需要，我们完全可以利用装饰模式，

组合两个已有的独立类成为一个组合类，

将计算财富价值的方法做稍微的改动

<?php
abstract class Tile{
abstract function getWealthFactor();
}

//平原类，wealthfactor为财富值
class Plains extends Tile{
private $wealthfactor=2;

function getWealthFactor(){
return $this->wealthfactor;
}
}

//含钻石土地类
class DiamondPlains extends Plains{

protected $tile;
function __construct(Tile $tile){
$this->tile=$tile;
}

function getWealthFactor(){
return parent::getWealthFactor()+2+$this->tile->getWealthFactor();
}
}

//污染土地类
class PollutedPlains extends Plains{

protected $tile;
function __construct(Tile $tile){
$this->tile=$tile;
}

function getWealthFactor(){
return parent::getWealthFactor()-4+$this->tile->getWealthFactor();
}
}

//净化土地类
class PurePlains extends Plains{

protected $tile;
function __construct(Tile $tile){
$this->tile=$tile;
}

function getWealthFactor(){
return parent::getWealthFactor()+4+$this->tile->getWealthFactor();
}
}

//创建一个污染含钻石的净化土地类
$tile=new DiamondPlains(new PollutedPlains(new PurePlains()));
echo $tile->getWealthFactor();</span>