[GitHub] [rocketmq] XiaoyiPeng commented on pull request #3534: [ISSUE #3533] optimize: It is better to specify the initialCapacity when initializing a HashMap as a local variable that will not add elements in the future.

[GitBox <gi...@apache.org>]

XiaoyiPeng commented on pull request #3534:
URL: https://github.com/apache/rocketmq/pull/3534#issuecomment-981662904


   > In my opinion, setting loadFactor=1 is not a good way, the default value can satisfy most scenarios.
   
   Here is using the style of the previous version code(like `org.apache.rocketmq.broker.filter.MessageEvaluationContext#keyValues()` ),as shown below:
   ```java
   public Map<String, Object> keyValues() {
           if (properties == null) {
               return null;
           }
   
           Map<String, Object> copy = new HashMap<String, Object>(properties.size(), 1);
   
           for (String key : properties.keySet()) {
               copy.put(key, properties.get(key));
           }
   
           return copy;
       }
   ```
   
    because we know exactly how many elements this map is going to put in, and we don't want  the map be expansioned(`resize`).
   
   


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