lambda常用的流操作

1.collect 根据stream里面的值生成一个列表

collect方法通常结合Collector结合一起使用，是一个通用的强大结构，可以满足数据转换、数据分组、字符串处理等操作

生成集合：

List<String,Object> list=Stream.of("a","b","c").collect(Collectors.toList())

集合转换：

TreeSet<String> treeSet=list.stream().collect(Collectors.toCollection(TreeSet::new));

转换成值：

List<Integer> list=stream.of("a","b","c").collect(Collectors.toList());
String maxChar=list.stream().collect(Collectors.maxBy(String::compare));

数据分块

List<Integer> collected=Stream.of(1,2,3,4,5,6,7).collect(Collectors.toList())
Map<Boolean,List<Integer>> divided=collected.stream().collect(Collectors.partitionBy(e -> e>5));

字符串处理

List<String> list=Stream.of("a","b","c").collect(Collectors.toList())
String format=list.stream().collect(Collectors.joining(",","[","]"))    

2.map 将数据流中的对象转化为一个新的流对象

List<String> collected=Stream.of("a","b","c").collect(Collectors.toList());
List<String> upperList = collected.stream().map(e-> e.toUpperCase()).collect(Collectors.toList());

3.flatmap 与map功能类似，只不过map对应的是一个流，而flatmap可以对应多个流

List<String> collected=Stream.of("a","b","c").collect(Collectors.toList());
List<String> collected2=Stream.of("c","d","e").collect(Collectors.toList());
List<List<String>> strSet=Arrays.asList(collected,collected2);
List<String> flatMap=strSet.stream().flatMap(plist -> plist.stream().collect(Collectors.toList());

4.filter 通过过滤条件筛选流中的对象

List<Integer> collected=Stream.of(1,2,3,4,5,6,7).collect(Collectors.toList())
List<Integer> nums=collected.stream().filter(e ->e>5).collect(Collectors.toList));    

5.max/min 求最大值和最小值

List<Integer> collected=Stream.of(1,2,3,4,5,6,7).collect(Collectors.toList())
Integer max=number.stream().max(Comparator.comparing(k ->k)).get();
Integer min=number.stream().min(Comparator.comparing(k ->k)).get();

6.reduce 从流中生成一个值

int sum =Stream.of(1,2,3,4,5,6,7).reduce(0,(acc,e) -> acc+ e)