class UserPo {
private String name;
private Double score;
}
List<UserPo> list = new ArrayList<>();
list.add(new UserPo("小一", 10.d));
list.add(new UserPo("小五", 50.d));
list.add(new UserPo("小六", 60.d));
list.add(new UserPo("小6", 60.d));
list.add(new UserPo("小空", null));
list.add(new UserPo("小九", 90.d));
long count = 0;
List<UserPo> filterList = null;
// filter 过滤器的使用
// 筛选出成绩不为空的学生人数
count = list.stream().filter(p -> null != p.getScore()).count();
System.out.println("参加考试的学生人数：" + count);
// collect
// 筛选出成绩不为空的学生集合
filterList = list.stream().filter(p -> null != p.getScore()).collect(Collectors.toList());
System.out.println("参加考试的学生信息：");
filterList.stream().forEach(System.out::println);
// map 将集合映射为另外一个集合
// 取出所有学生的成绩
List<Double> scoreList = list.stream().map(p -> p.getScore()).collect(Collectors.toList());
System.out.println("所有学生的成绩集合：" + scoreList);
// map
System.out.println("按学生成绩归集：");
Map<Double, List<UserPo>> groupByScoreMap = list.stream().filter(p -> null != p.getScore()).collect(Collectors.groupingBy(UserPo::getScore));
for (Map.Entry<Double, List<UserPo>> entry : groupByScoreMap.entrySet()) {
System.out.println("成绩：" + entry.getKey() + " 人数：" + entry.getValue().size());
}
// 将学生姓名集合串成字符串，用逗号分隔
String nameString = list.stream().map(p -> p.getName()).collect(Collectors.joining(","));
System.out.println("所有学生的姓名字符串：" + nameString);
// sorted排序
// 按学生成绩逆序排序 正序则不需要加.reversed()
filterList = list.stream().filter(p -> null != p.getScore()).sorted(Comparator.comparing(UserPo::getScore).reversed()).collect(Collectors.toList());
System.out.println("所有学生的成绩集合，逆序排序：");
filterList.stream().forEach(System.out::println);
// forEach
filterList.stream().forEach(p -> p.setScore(p.getScore() + 10));
System.out.println("及格人数太少，给每个人加10分");
filterList.stream().forEach(System.out::println);
// count
count = filterList.stream().filter(p -> p.getScore() >= 60).count();
System.out.println("最后及格人数" + count);
DoubleSummaryStatistics statistics = filterList.stream().mapToDouble(p -> p.getScore()).summaryStatistics();
System.out.println("列表中最大的数 : " + statistics.getMax());
System.out.println("列表中最小的数 : " + statistics.getMin());
System.out.println("所有数之和 : " + statistics.getSum());
System.out.println("平均数 : " + statistics.getAverage());
// 并行流 使用
count = list.parallelStream().filter(p -> null != p.getScore()).count();
System.out.println("并行流处理参加考试的学生人数：" + count);
// BigDecimal 求和
// BigDecimal baseQtySum = stkInventories.stream().map(StkInventory::getBaseQty).reduce(BigDecimal.ZERO, BigDecimal::add);
List<Person> personList = new ArrayList<Person>();
personList.add(new Person("Tom", 10, 23, "male", "New York", null));
personList.add(new Person("Tom", 11, 23, "male", "Washington1", null));
personList.add(new Person("Tom", 11, 21, "female", "Washington", null));
personList.add(new Person("Anni", 110, 24, "female", "New York", null));
personList.add(new Person("Alisa", 111, 26, "male", "New York", null));
personList.add(new Person("Alisa", 111, 25, "female", "New York", null));
//根据一个属性合并
// List<Person> result = new ArrayList<>(personList.stream()
// .collect(Collectors.toMap(Person::getName, a -> a, (o1, o2) -> {
// o1.setSalary(o1.getSalary() + o2.getSalary());
// return o1;
// })).values());
// result.forEach(System.out::println);
//根据两个属性合并
// List<Person> list = new ArrayList<>();
// personList.parallelStream().collect(Collectors.groupingBy(o->(o.getName() + o.getAge() + o.getArea()),Collectors.toList()))
// .forEach((id,transfer) -> transfer.stream().reduce((a, b) ->
// new Person(a.getName(), a.getAge(),a.getSalary() + b.getSalary(), a.getSex(), a.getArea(), null))
// .ifPresent(list::add));
//
// list.forEach(System.out::println);
// 设置第三属性分组再合并
personList.forEach(a -> a.setNameAge(a.getName() + a.getAge()));
List<Person> result1 = new ArrayList<>(personList.stream()
.collect(Collectors.toMap(Person::getNameAge, a -> a, (o1, o2) -> {
o1.setSalary(o1.getSalary() + o2.getSalary());
return o1;
})).values());
result1.forEach(System.out::println);