Java 8 stream的详细用法
话不多说,直接看代码演示
/** * @description: stream 练习 * @author: hwx * @date: 2022/02/10 **/ public class stream { static class Person { private String name; // 姓名 private int salary; // 薪资 private int age; // 年龄 private String sex; //性别 private String area; // 地区 // 构造方法 public Person(String name, int salary, int age,String sex,String area) { this.name = name; this.salary = salary; this.age = age; this.sex = sex; this.area = area; } public Person(String name, int salary, String sex, String area) { this.name = name; this.salary = salary; this.sex = sex; this.area = area; } // 省略了get和set，请自行添加 public String getName() { return name; } public void setName(String name) { this.name = name; } public int getSalary() { return salary; } public void setSalary(int salary) { this.salary = salary; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public String getArea() { return area; } public void setArea(String area) { this.area = area; } @Override public String toString() { return "Person{" + "name='" + name + '\'' + ", salary=" + salary + ", age=" + age + ", sex='" + sex + '\'' + ", area='" + area + '\'' + '}'; } } public static void main(String[] args) { List<Person> personList = new ArrayList<Person>(); personList.add(new Person("Tom", 8900, "male", "New York")); personList.add(new Person("Tom", 8800, "male", "New York")); personList.add(new Person("Jack", 7000, "male", "Washington")); personList.add(new Person("Lily", 7800, "female", "Washington")); personList.add(new Person("Anni", 8200, "female", "New York")); personList.add(new Person("Owen", 9500, "male", "New York")); personList.add(new Person("Alisa", 7900, "female", "New York")); //遍历输出符合条件的元素 personList.stream().filter(e -> e.salary > 8000).forEach(System.out::println); //筛选薪资大于8000的 List<Person> collect = personList.stream().filter(e -> e.salary > 8000).collect(Collectors.toList()); // List<Person> collect22 = personList.stream().filter(e -> e::getSalary>8000).collect(Collectors.toList()); Set<Person> collect1 = personList.stream().filter(e -> e.salary > 8000).collect(Collectors.toSet()); //去重 Map<String, Integer> collect2 = personList.stream().filter(e -> e.salary > 8000).collect(Collectors.toMap(e -> e.name, e -> e.salary,(a1,a2)->a2)); //.map用法 List<String> collect3 = personList.stream().filter(e -> e.salary > 8000).map(e -> e.name).collect(Collectors.toList()); // 匹配第一个 Optional<Person> first = personList.stream().filter(e -> e.salary > 8000).findFirst(); // 匹配任意（适用于并行流） Optional<Person> first1 = personList.parallelStream().filter(e -> e.salary > 8000).findFirst(); // 是否包含符合特定条件的元素 boolean b = personList.stream().anyMatch(e -> e.salary > 8000); System.out.println(collect); System.out.println(collect1); System.out.println(collect2); System.out.println(collect3); System.out.println("匹配第一个"+first); System.out.println("匹配任意（适用于并行流）"+first1); System.out.println("是否包含符合特定条件的元素"+b); //筛选出名字最长的 Optional<Person> max = personList.stream().max(Comparator.comparing(e -> e.name.length())); //筛选出工资最高的 Optional<Person> max1 = personList.stream().max(Comparator.comparing(e -> e.salary)); System.out.println("筛选出名字最长的"+max); System.out.println("筛选出工资最高的"+max1); //筛选出工资大于8000的总人数 long count = personList.stream().filter(e -> e.salary > 8000).count(); System.out.println("筛选出工资大于8000的总人数"+count); String[] strArr = { "abcd", "bcdd", "defde", "fTr" }; //英文字符串数组的元素全部改为大写 List<String> collect4 = Arrays.stream(strArr).map(String::toUpperCase).collect(Collectors.toList()); System.out.println("英文字符串数组的元素全部改为大写"+collect4); List<Integer> intList = Arrays.asList(1, 3, 5, 7, 9, 11); //整数数组每个元素+3 List<Integer> collect5 = intList.stream().map(e -> e + 3).collect(Collectors.toList()); System.out.println("整数数组每个元素+3"+collect5); //将员工的薪资全部增加1000。 List<Integer> collect6 = personList.stream().map(e -> e.salary + 1000).collect(Collectors.toList()); System.out.println("将员工的薪资全部增加1000"+collect6); List<Person> collect7 = personList.stream().map(e -> { Person person = new Person(e.name, e.salary, e.sex, e.area); person.setSalary(person.salary + 1000); return person; }).collect(Collectors.toList()); System.out.println("(不改变原先结构)将员工的薪资全部增加1000"+collect7); /* List<Person> collect8 = personList.stream().map(e -> { e.setSalary(e.salary + 1000); return e; }).collect(Collectors.toList()); System.out.println("(不改变原先结构)将员工的薪资全部增加1000(原先的list被改变)"+collect8);*/ //将两个字符数组合并成一个新的字符数组 List<String> list = Arrays.asList("m,k,l,a", "1,3,5,7"); List<String> collect9 = list.stream().flatMap(e -> { // 将每个元素转换成一个stream String[] split = e.split(","); Stream<String> s2 = Arrays.stream(split); return s2; }).collect(Collectors.toList()); System.out.println("将两个字符数组合并成一个新的字符数组"+collect9); //求所有员工的工资之和 Optional<Integer> reduce = personList.stream().map(Person::getSalary).reduce(Integer::sum); System.out.println("求所有员工的工资之和"+reduce); Integer reduce1 = personList.stream().reduce(0, (sum, p) -> sum += p.getSalary(), (sum1, sum2) -> sum1 + sum2); System.out.println("求所有员工的工资之和"+reduce1); Integer sumSalary3 = personList.stream().reduce(0, (sum, p) -> sum += p.getSalary(), Integer::sum); System.out.println("求所有员工的工资之和"+sumSalary3); // 求员工总数 Long collect10 = personList.stream().collect(Collectors.counting()); System.out.println("求员工总数"+collect10); // 求平均工资 Double collect11 = personList.stream().collect(Collectors.averagingDouble(Person::getSalary)); System.out.println("求平均工资"+collect11); // 求最高工资 Optional<Integer> collect12 = personList.stream().map(Person::getSalary).collect(Collectors.maxBy(Integer::compare)); System.out.println("求最高工资"+collect12); // 求工资之和 Integer sum = personList.stream().collect(Collectors.summingInt(Person::getSalary)); System.out.println("员工工资总和：" + sum); // 一次性统计所有信息 DoubleSummaryStatistics collect13 = personList.stream().collect(Collectors.summarizingDouble(Person::getSalary)); System.out.println("员工工资所有统计：" + collect13); //分组 // 将员工按薪资是否高于8000分组 Map<Boolean, List<Person>> collect8 = personList.stream().collect(Collectors.partitioningBy(e -> e.getSalary() > 8000)); System.out.println("将员工按薪资是否高于8000分组"+collect8); // 将员工按性别分组 Map<String, List<Person>> collect14 = personList.stream().collect(Collectors.groupingBy(Person::getSex)); System.out.println("将员工按性别分组"+collect14); // 将员工先按性别分组，再按地区分组 Map<String, Map<String, List<Person>>> group2 = personList.stream().collect(Collectors.groupingBy(Person::getSex, Collectors.groupingBy(Person::getArea))); System.out.println("将员工先按性别分组，再按地区分组"+group2); //接合 String names = personList.stream().map(p -> p.getName()).collect(Collectors.joining(",")); System.out.println("所有员工的姓名：" + names); //排序 // 按工资升序排序（自然排序） List<String> newList = personList.stream().sorted(Comparator.comparing(Person::getSalary)).map(Person::getName) .collect(Collectors.toList()); System.out.println("按工资升序排序（自然排序）"+newList); // 按工资倒序排序 List<String> newList2 = personList.stream().sorted(Comparator.comparing(Person::getSalary).reversed()) .map(Person::getName).collect(Collectors.toList()); System.out.println("按工资倒序排序"+newList); // 先按工资再按年龄升序排序 List<String> newList3 = personList.stream() .sorted(Comparator.comparing(Person::getSalary).thenComparing(Person::getAge)).map(Person::getName) .collect(Collectors.toList()); System.out.println("先按工资再按年龄升序排序：" + newList3); // 先按工资再按年龄自定义排序（降序） List<String> newList4 = personList.stream().sorted((p1, p2) -> { if (p1.getSalary() == p2.getSalary()) { return p2.getAge() - p1.getAge(); } else { return p2.getSalary() - p1.getSalary(); } }).map(Person::getName).collect(Collectors.toList()); System.out.println("先按工资再按年龄自定义降序排序：" + newList4); String[] arr1 = { "a", "b", "c", "d" }; String[] arr2 = { "d", "e", "f", "g" }; Stream<String> stream1 = Stream.of(arr1); Stream<String> stream2 = Stream.of(arr2); // concat:合并两个流 distinct：去重 List<String> newList8 = Stream.concat(stream1, stream2).distinct().collect(Collectors.toList()); // limit：限制从流中获得前n个数据 List<Integer> collect88 = Stream.iterate(1, x -> x + 2).limit(10).collect(Collectors.toList()); // skip：跳过前n个数据 List<Integer> collect888 = Stream.iterate(1, x -> x + 2).skip(1).limit(5).collect(Collectors.toList()); System.out.println("流合并：" + newList8); System.out.println("limit：" + collect88); System.out.println("skip：" + collect888); } }
