public void setReason(java.util.Collection<String> reason) {
        if (reason == null) {
            this.reason = null;
            return;
        }

        this.reason = new java.util.ArrayList<String>(reason);
    }
<p>
If you use User-Personalization-v2, a list of reasons for why the item was included in recommendations. Possible
reasons include the following:
</p>
<ul>
<li>
<p>
Promoted item - Indicates the item was included as part of a promotion that you applied in your recommendation
request.
</p>
</li>
<li>
<p>
Exploration - Indicates the item was included with exploration. With exploration, recommendations include items
with less interactions data or relevance for the user. For more information about exploration, see <a
href="https://docs.aws.amazon.com/personalize/latest/dg/use-case-recipe-features.html#about-exploration"
>Exploration</a>.
</p>
</li>
<li>
<p>
Popular item - Indicates the item was included as a placeholder popular item. If you use a filter, depending on
how many recommendations the filter removes, Amazon Personalize might add placeholder items to meet the
<code>numResults</code> for your recommendation request. These items are popular items, based on interactions
data, that satisfy your filter criteria. They don't have a relevance score for the user.
</p>
</li>
</ul>

@param reason
       If you use User-Personalization-v2, a list of reasons for why the item was included in recommendations.
       Possible reasons include the following:</p>
       <ul>
       <li>
       <p>
       Promoted item - Indicates the item was included as part of a promotion that you applied in your
       recommendation request.
       </p>
       </li>
       <li>
       <p>
       Exploration - Indicates the item was included with exploration. With exploration, recommendations include
       items with less interactions data or relevance for the user. For more information about exploration, see
       <a
       href="https://docs.aws.amazon.com/personalize/latest/dg/use-case-recipe-features.html#about-exploration"
       >Exploration</a>.
       </p>
       </li>
       <li>
       <p>
       Popular item - Indicates the item was included as a placeholder popular item. If you use a filter,
       depending on how many recommendations the filter removes, Amazon Personalize might add placeholder items
       to meet the <code>numResults</code> for your recommendation request. These items are popular items, based
       on interactions data, that satisfy your filter criteria. They don't have a relevance score for the user.
       </p>
       </li>
aws-java-sdk-personalizeruntime/src/main/java/com/amazonaws/services/personalizeruntime/model/PredictedItem.java