Java Stream函数式编程管道流结果处理

List<String> nameStrs = Arrays.asList("Monkey", "Lion", "Giraffe","Lemur");
List<String> list = nameStrs.stream()
        .filter(s -> s.startsWith("L"))
        .map(String::toUpperCase)
        .sorted()
        .collect(toList());
System.out.println(list);

Stream.of("Monkey", "Lion", "Giraffe", "Lemur", "Lion")
        .parallel()
        .forEach(System.out::println);
Stream.of("Monkey", "Lion", "Giraffe", "Lemur", "Lion")
        .parallel()
        .forEachOrdered(System.out::println);

Set<String> collectToSet = Stream.of(
   "Monkey", "Lion", "Giraffe", "Lemur", "Lion"
) 
.collect(Collectors.toSet());

//最终collectToSet 中的元素是:[Monkey, Lion, Giraffe, Lemur]，注意Set会去重。

List<String> collectToList = Stream.of(
   "Monkey", "Lion", "Giraffe", "Lemur", "Lion"
).collect(Collectors.toList());
// 最终collectToList中的元素是: [Monkey, Lion, Giraffe, Lemur, Lion]

LinkedList<String> collectToCollection = Stream.of(
   "Monkey", "Lion", "Giraffe", "Lemur", "Lion"
).collect(Collectors.toCollection(LinkedList::new));
//最终collectToCollection中的元素是: [Monkey, Lion, Giraffe, Lemur, Lion]

String[] toArray = Stream.of(
   "Monkey", "Lion", "Giraffe", "Lemur", "Lion"
) .toArray(String[]::new);
//最终toArray字符串数组中的元素是: [Monkey, Lion, Giraffe, Lemur, Lion]

Map<String, Integer> toMap = Stream.of(
    "Monkey", "Lion", "Giraffe", "Lemur", "Lion"
)
.distinct()
.collect(Collectors.toMap(
       Function.identity(),   //元素输入就是输出，作为key
       s -> (int) s.chars().distinct().count()// 输入元素的不同的字母个数，作为value
));
// 最终toMap的结果是: {Monkey=6, Lion=4, Lemur=5, Giraffe=6}   

Map<Character, List<String>> groupingByList =  Stream.of(
    "Monkey", "Lion", "Giraffe", "Lemur", "Lion"
)
.collect(Collectors.groupingBy(
       s -> s.charAt(0) ,  //根据元素首字母分组，相同的在一组
       // counting()        // 加上这一行代码可以实现分组统计
));
// 最终groupingByList内的元素: {G=[Giraffe], L=[Lion, Lemur, Lion], M=[Monkey]}
//如果加上counting() ，结果是:  {G=1, L=3, M=1}

boolean containsTwo = IntStream.of(1, 2, 3).anyMatch(i -> i == 2);
// 判断管道中是否包含2，结果是: true
long nrOfAnimals = Stream.of(
    "Monkey", "Lion", "Giraffe", "Lemur"
).count();
// 管道中元素数据总计结果nrOfAnimals: 4
int sum = IntStream.of(1, 2, 3).sum();
// 管道中元素数据累加结果sum: 6
OptionalDouble average = IntStream.of(1, 2, 3).average();
//管道中元素数据平均值average: OptionalDouble[2.0]
int max = IntStream.of(1, 2, 3).max().orElse(0);
//管道中元素数据最大值max: 3
IntSummaryStatistics statistics = IntStream.of(1, 2, 3).summaryStatistics();
// 全面的统计结果statistics: IntSummaryStatistics{count=3, sum=6, min=1, average=2.000000, max=3}