如何使用JAVA 8从map获取第一个键值？

Question

As for now I am doing :

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 ?

Answer 1

I see two problems with your method:

• it will throw an exception if the map is empty
• a HashMap , for example, has no order - so your method is really more of a getAny() than a getNext() .

With a stream you could use either:

//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 .

Answer 2

Seems like you need findFirst here

   Optional<Map.Entry<Item, Boolean>> firstEntry =    
        processedItem.entrySet().stream().findFirst();

Obviously a HashMap has no order, so findFirst might return a different result on different calls. Probably a more suitable method would be findAny for your case.