Java8新特性中常用的去重、交集、差集、排序等功能_java新特性 去重

1. 集合去重：
List<String> strList = list.stream().distinct().collect(Collectors.toList());
List<Student> list = Students.stream().collect(collectingAndThen(toCollection(() -> new TreeSet<>(comparingLong(Student::getId))), ArrayList::new));//对象集合去重
2.交集
List<String> strList = strList1.stream().filter(str->strList2.contains(str)).collect(Collectors.toList);
List<Student> students= students1.stream().filter(item ->students2.stream().map(e -> e.getName()).collect(Collectors.toList()).contains(item.getName())).collect(Collectors.toList());//对象集合求交集
3.差集
List<String> strList = strList1.stream().filter(str->!strList2.contains(str)).collect(Collectors.toList);
List<Student> students= students1.stream().filter(item -> !students2.stream().map(e -> e.getName()).collect(Collectors.toList()).contains(item.getName())).collect(Collectors.toList());//对象集合求差集
4.排序
students.sort(Comparator.comparing(Student::getId).thenComparing(Student::getName));//对象集合升序排序
students.sort(Comparator.comparing(Student::getId).reversed().thenComparing(Student::getName));//对象集合倒序排序
5.List转化Map
Map<String, Student> studentMap = students.parallelStream().collect(Collectors.toMap(Student::getId, Function.identity(), (v1, v2) -> v2));//对象集合转Map
6.获取list对象的某个字段组装成新list
List<String> studentIdList = students.stream().map(student-> student.getId()).collect(Collectors.toList());
7.求最值
int minAge = students.stream().map(Student::getAge).min(Integer::compareTo).get();//最小值
int maxAge = students.stream().map(Student::getAge).max(Integer::compareTo).get();//最大值
8.求和
int sumAge = students.stream().mapToInt(Student::getAge).sum();//基本类型
9.分组
Map<String, List<Student>> groupBySex = students.stream().collect(Collectors.groupingBy(Student::getSex));//按性别分组 
10.forEach循环：
forEach循环可以用return做跳过操作，而不能用break(会在编译期报错)；
11.Comparator.comparing排序：
Comparator.comparing默认是升序排序，可以用reversed改成降序
students.sort(Comparator.comparingLong(Student::getAge));
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