output:
-2
点评：不具有灵活性，我们不能同时获得钻石与被污染的土地的资金情况。
装饰模式使用组合和委托而不是只使用继承来解决功能变化的问题。
看例子：
<?php
abstract class Tile {
abstract function getWealthFactor();
}
class Plains extends Tile {
private $wealthfactor = 2;
function getWealthFactor() {
return $this->wealthfactor;
}
}
abstract class TileDecorator extends Tile { // 装饰
protected $tile;
function __construct( Tile $tile ) {
$this->tile = $tile;
}
}
class DiamondDecorator extends TileDecorator { // 钻石装饰
function getWealthFactor() {
return $this->tile->getWealthFactor()+2;
}
}
class PollutionDecorator extends TileDecorator { // 污染装饰
function getWealthFactor() {
return $this->tile->getWealthFactor()-4;
}
}
$tile = new Plains();
print $tile->getWealthFactor(); // 2
$tile = new DiamondDecorator( new Plains() );
print $tile->getWealthFactor(); // 4
$tile = new PollutionDecorator(
new DiamondDecorator( new Plains() ));
print $tile->getWealthFactor(); // 0
?>
output:
2
4
0
点评：这个模型具有扩展性。我们不需要创建DiamondPollutionPlains对象就可以构建一个钻石被污染的对象。
一个更逼真的例子
<?php
class RequestHelper{} // 请求助手
abstract class ProcessRequest { // 进程请求
abstract function process( RequestHelper $req );
}
class MainProcess extends ProcessRequest { // 主进程
function process( RequestHelper $req ) {
print __CLASS__.": doing something useful with requestn";
}
}
abstract class DecorateProcess extends ProcessRequest { // 装饰进程
protected $processrequest;
function __construct( ProcessRequest $pr ) { // 引用对象，委托
$this->processrequest = $pr;
}
}
class LogRequest extends DecorateProcess { // 日志请求
function process( RequestHelper $req ) {
print __CLASS__.": logging requestn"; // 当前类,有点递归的感觉
$this->processrequest->process( $req );
}
}
class AuthenticateRequest extends DecorateProcess { // 认证请求
function process( RequestHelper $req ) {
print __CLASS__.": authenticating requestn";
$this->processrequest->process( $req );
}
}
class StructureRequest extends DecorateProcess { // 组织结构请求
function process( RequestHelper $req ) {
print __CLASS__.": structuring requestn";
$this->processrequest->process( $req );
}
}
$process = new AuthenticateRequest( new StructureRequest(
new LogRequest (
new MainProcess()
))); // 这样可以很灵活的组合进程的关系，省去很多重复的继承
$process->process( new RequestHelper() );
print_r($process);
?>
output:
AuthenticateRequest: authenticating request
StructureRequest: structuring request
LogRequest: logging request
MainProcess: doing something useful with request
AuthenticateRequest Object
(
[processrequest:protected] => StructureRequest Object
(
[processrequest:protected] => LogRequest Object
(
[processrequest:protected] => MainProcess Object
(
)
)
)
)
