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<p class="MsoPlainText">I ran into the java.util.ConcurrentModificationException too when trying to iterate over an ArrayList created via "from collect" in Drools 5.5.0 Final. My solution was to copy the list into an array using List.toArray and then iterate
over that. I found that the type information is often not properly maintained in the right-hand side of the rule, requiring casts where they should be unnecessary. Here is a complete, self-contained example that shows how to iterate over the array to modify
or retract the facts.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">import</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black"> java.util.ArrayList;</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">declare</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black"> Fact</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> @propertyReactive</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> name : String @key</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> value : String</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">end</span></b><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">rule</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><span style="font-size:10.0pt;font-family:Consolas;color:green">"initialize"</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">when</span></b><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">then</span></b><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">insert</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black"> (</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">new</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
Fact(</span><span style="font-size:10.0pt;font-family:Consolas;color:green">"abc"</span><span style="font-size:10.0pt;font-family:Consolas;color:black">));</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">insert</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black"> (</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">new</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
Fact(</span><span style="font-size:10.0pt;font-family:Consolas;color:green">"def"</span><span style="font-size:10.0pt;font-family:Consolas;color:black">));</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">insert</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black"> (</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">new</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
Fact(</span><span style="font-size:10.0pt;font-family:Consolas;color:green">"ghi"</span><span style="font-size:10.0pt;font-family:Consolas;color:black">));</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">end</span></b><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">rule</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><span style="font-size:10.0pt;font-family:Consolas;color:green">"collect and retract"</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">salience</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black"> 1</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">when</span></b><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> $list : ArrayList(size > 0)
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">from</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">collect</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black"> (Fact(name
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">in</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black"> (</span><span style="font-size:10.0pt;font-family:Consolas;color:green">"abc"</span><span style="font-size:10.0pt;font-family:Consolas;color:black">,
</span><span style="font-size:10.0pt;font-family:Consolas;color:green">"def"</span><span style="font-size:10.0pt;font-family:Consolas;color:black">)))</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">then</span></b><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><span style="font-size:10.0pt;font-family:Consolas;color:olive">// This will not compile without the explicit cast.</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> Fact[] facts = (Fact[]) $list.toArray(</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">new</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
Fact[0]);</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> </span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> </span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">for</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
(Fact f : facts) {</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">retract</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black"> (f);</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> }</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">end</span></b><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">rule</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><span style="font-size:10.0pt;font-family:Consolas;color:green">"collect and modify"</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">salience</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black"> 2</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">when</span></b><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> $list : ArrayList(size > 0)
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">from</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">collect</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black"> (Fact(name
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">in</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black"> (</span><span style="font-size:10.0pt;font-family:Consolas;color:green">"abc"</span><span style="font-size:10.0pt;font-family:Consolas;color:black">,
</span><span style="font-size:10.0pt;font-family:Consolas;color:green">"def"</span><span style="font-size:10.0pt;font-family:Consolas;color:black">)))</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">then</span></b><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> Fact[] facts = (Fact[]) $list.toArray(</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">new</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
Fact[0]);</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> </span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">for</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
(Fact f : facts) {</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><span style="font-size:10.0pt;font-family:Consolas;color:olive">// The modify will not compile without an explicit cast,</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><span style="font-size:10.0pt;font-family:Consolas;color:olive">// despite the declaration of f in the enhanced for loop.</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> Fact g = (Fact) f;</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> </span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">modify</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
(g) {</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> setValue(g.getName() +
</span><span style="font-size:10.0pt;font-family:Consolas;color:green">" A"</span><span style="font-size:10.0pt;font-family:Consolas;color:black">);</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> }</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> }</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><span style="font-size:10.0pt;font-family:Consolas;color:olive">// Avoid the cast by using a traditional indexed loop.</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">for</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black"> (</span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">int</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
i = 0; i < facts.length; i++) {</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><span style="font-size:10.0pt;font-family:Consolas;color:olive">// Copy the array element into a new variable</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><span style="font-size:10.0pt;font-family:Consolas;color:olive">// because "modify (facts[i])" will not compile.</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> Fact g = facts[i];</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> </span><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">modify</span></b><span style="font-size:10.0pt;font-family:Consolas;color:black">
(g) {</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> setValue(g.getName() +
</span><span style="font-size:10.0pt;font-family:Consolas;color:green">" B"</span><span style="font-size:10.0pt;font-family:Consolas;color:black">);</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> }</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Consolas;color:black"> }</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:10.0pt;font-family:Consolas;color:#960000">end</span></b><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Best wishes,<o:p></o:p></p>
<p class="MsoPlainText">Tom<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">-----Original Message-----<br>
From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of radhika.inugala<br>
Sent: Tuesday, July 02, 2013 3:20 PM<br>
To: rules-users@lists.jboss.org<br>
Subject: Re: [rules-users] drools migration</p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Also I am looking at the domain objects for this:<o:p></o:p></p>
<p class="MsoPlainText">And I need to retract all the objects with locationType == LocationType.ORIGIN the fromState is one of them.<o:p></o:p></p>
<p class="MsoPlainText">But there would be more of the same.<o:p></o:p></p>
<p class="MsoPlainText">I think that is the reason the collect is in there.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">--<o:p></o:p></p>
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