如何使用 JAVA 8 从地图中获取第一个键值？
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How to get the first key value from map using JAVA 8?
提问by user3407267
As for now I am doing :
至于现在我在做什么：
Map<Item, Boolean> processedItem = processedItemMap.get(i);
Map.Entry<Item, Boolean> entrySet = getNextPosition(processedItem);
Item key = entrySet.getKey();
Boolean value = entrySet.getValue();
public static Map.Entry<Item, Boolean> getNextPosition(Map<Item, Boolean> processedItem) {
return processedItem.entrySet().iterator().next();
}
Is there any cleaner way to do this with java8 ?
有没有更干净的方法可以用 java8 做到这一点？
回答by assylias
I see two problems with your method:
我发现你的方法有两个问题：
- it will throw an exception if the map is empty
- a
HashMap, for example, has no order - so your method is really more of agetAny()than agetNext().
- 如果地图为空，它将抛出异常
HashMap例如，a没有顺序 - 所以你的方法实际上getAny()比 a更像是agetNext()。
With a stream you could use either:
对于流，您可以使用：
//if order is important, e.g. with a TreeMap/LinkedHashMap
map.entrySet().stream().findFirst();
//if order is not important or with unordered maps (HashMap...)
map.entrySet().stream().findAny();
which returns an Optional.
它返回一个Optional.
回答by Eugene
Seems like you need findFirsthere
好像你需要findFirst这里
Optional<Map.Entry<Item, Boolean>> firstEntry =
processedItem.entrySet().stream().findFirst();
Obviously a HashMaphas no order, so findFirst might return a different result on different calls. Probably a more suitable method would be findAnyfor your case.
显然 aHashMap没有顺序，因此 findFirst 可能会在不同的调用中返回不同的结果。可能更适合findAny您的情况的方法。
