执行及描述任务-------访问者模式

UMl类

代码实现

<?php
//visitor.php 访问者模式

abstract class Unit{
    protected $depth;
    function accept(ArmyVisitor $visitor){
        $method = "visit".get_class($this);
        $visitor->$method($this);
    }

    protected function setDepth($depth){
        $this->depth = $depth;
    }

    function getDepth(){
        return $this->depth;
    }

    function getComposite(){
        return null;
    }
    abstract function bombardStrengrg();
}

abstract class CompositeUnit extends Unit{
    protected $unit = array();

    function getComposite(){
        return $this;
    }


    function removeUnit(Unit $unit){
        $this->unit = array_udiff($this->unit,array($unit),
            function($a,$b){return ($a===$b)?0:1;});
    }

    function addUnit(Unit $unit){
        if(in_array($unit,$this->unit,true)){
            return;
        }
        $unit->setDepth($this->depth+1);
        $this->unit[] = $unit;
    }

    function accept(ArmyVisitor $visitor){
        parent::accept($visitor);
        foreach ($this->unit as $thisunit) {
            $thisunit->accept($visitor);
        }
    }
}

class Army extends CompositeUnit{
    function bombardStrengrg(){
        $ret = 0;
        foreach ($this->unit as $unit) {
            $ret+=$unit->bombardStrengrg();
        }
        return $ret;
    }
}

class Archer extends Unit{
    function bombardStrengrg(){
        return 4;
    }
}

class LaserCannon extends Unit{
    function bombardStrengrg(){
        return 5;
    }
}

abstract class ArmyVisitor{
    abstract function visit(Unit $node);
    function visitArcher(Archer $node){
        $this->visit($node);
    }

    

    function visitLaserCannon(LaserCannon  $node){
        $this->visit($node);
    }

    function visitTroopCarrierUnit(TroopCarrierUnit $node){
        $this->visit($node);
    }

    function visitArmy(Army $node){
        $this->visit($node);
    }
}

class TextDumpArmyVisitor extends ArmyVisitor{
    private $text='';
    function visit(Unit $node){
        $ret = '';
        $pad = 4*$node->getDepth();
        $ret.=sprintf("%{$pad}s",'');
        $ret.=get_class($node).": ";
        $ret.="bombard: ".$node->bombardStrengrg()."<br>";
        $this->text.=$ret;
    }

    function getText(){
        return $this->text;
    }
}

class TaxCollectionVisitor extends ArmyVisitor{
    private $due=0;
    private $report=0;
    function visit(Unit $node){
        $this->levy($node,1);
    }

    function visitArcher(Archer $node){
        $this->levy($node,2);
    }

    function visitTroopCarrierUnit(TroopCarrierUnit $node){
        $this->levy($node,2);
    }

    function visitLaserCannon(LaserCannon $node){
        $this->levy($node,2);
    }

    function levy(Unit $unit,$amout){
        $this->report.="Tax levied for ".get_class($unit);
        $this->report.=": $amout<br>";
        $this->due+=$amout;
    }

    function getRepost(){
        return $this->report;
    }

    function getTax(){
        return $this->due;
    }
}

$main_army = new Army();
$main_army->addUnit(new Archer());
$main_army->addUnit(new LaserCannon());

//$textdump = new TextDumpArmyVisitor();
$taxcollector = new TaxCollectionVisitor();
$main_army->accept($taxcollector);
//echo $textdump->getText();
echo "TOTAL: ";
echo $taxcollector->getTax()."<br>";
echo $taxcollector->getRepost();
?>

问题

访问者可可以用于任何对象集合

外部化操作可能破坏封装，例如给TextdumpArmyVisitor对象提供信息，我们被迫给Unit接口提供了一个额外的方法