Java 8中如何获取Map对象的第一个元素

在Java 8中可以通过下面的方式获取Map对象的第一个元素：

1.获取元素键

//if order is important, e.g. with a TreeMap/LinkedHashMap
map.keySet().stream().findFirst();

//if order is not important or with unordered maps (HashMap...)
map.keySet().stream().findAny();

2.获取元素键值

//if order is important, e.g. with a TreeMap/LinkedHashMap
map.values().stream().findFirst();

//if order is not important or with unordered maps (HashMap...)
map.values().stream().findAny();

3.获取元素

//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();

References

1. How to get the first key value from map using JAVA 8?
2. Java中Map对象的values()/keySet()/entrySet()区别