额外字符串比较与hashmap查找的性能

假设我正在运行下面列出1000个的代码片段中的任何一个 Event 条目(in) allEventsToAggregate )如果事件发生在 所有事件到聚合 被排序 customerId ,每个客户大约有3个活动?这本质上是一个字符串比较的问题。 HashMap 查找性能。

选项1:

Map<String, List<Event>> eventsByCust = new HashMap<String, List<Event>>();
List<Event> thisCustEntries;
String lastCust = null;
for (Event thisEvent : allEventsToAggregate) {
    if (!thisEvent.getCustomerId().equals(lastCust)) {
        thisCustEntries = eventsByCust.get(thisEvent.getCustomerId());
        if (thisCustEntries == null) {
            thisCustEntries = new ArrayList<Event>();
        }
    }
    thisCustEntries.add(thisEvent);
    eventsByCust.put(thisEvent.getCustomerId(), thisCustEntries);
    lastCust = thisEvent.getCustomerId();
}

选项2:

Map<String, List<Event>> eventsByCust = new HashMap<String, List<Event>>();
for (Event thisEvent : allEventsToAggregate) {
    List<Event> thisCustEntries = eventsByCust.get(thisEvent.getCustomerId());
    if (thisCustEntries == null) {
        thisCustEntries = new ArrayList<Event>();
    }
    thisCustEntries.add(thisEvent);
}