网站添加js广告位,网站建设 报价单,wordpress 编辑器模板,企业网站的做本文完整测试代码见文末。测试数据是List里的4个员工对象实例#xff1a;根据员工所在的城市进行分组#xff1a;结果分成了三组#xff1a;第一组的员工在上海#xff1a;第二组的员工在成都#xff1a;统计每组员工个数#xff1a;把员工进行分组#xff0c;得分大于1…本文完整测试代码见文末。测试数据是List里的4个员工对象实例根据员工所在的城市进行分组结果分成了三组第一组的员工在上海第二组的员工在成都统计每组员工个数把员工进行分组得分大于101分的在一组小于等于101的在另一组分组结果package java8;import java.util.ArrayList;import java.util.List;import java.util.Map;import java.util.Map.Entry;import java.util.function.Consumer;import java.util.stream.Collectors;class Employee {private String city;private String name;private int score;public Employee(String name, String city, int score){this.city city;this.name name;this.score score;}public String getCity(){System.out.println(city: this.city);return this.city;}public String getName() {return this.name;}public int getScore() {return this.score;}Overridepublic String toString() {return String.format(Employee: this.name city: this.city);}}class Person {private String name;private int age;Person(String name, int age) {this.name name;this.age age;}Overridepublic String toString() {return String.format(Person{name%s, age%d}, name, age);}}// Jerry 2016-01-15 20:51PM ? 多用于extends generic的type接受所有Object的sub classpublic class StreamTest {private static void printMap(Map extends Object, ? extends Object map) {for(Entry extends Object, ? extends Object entry:map.entrySet()) {System.out.println(key entry.getKey() , Value entry.getValue());}}public static void main(String[] args) {ArrayList employees new ArrayList();employees.add(new Employee(A, Shanghai,100));employees.add(new Employee(B, Chengdu,101));employees.add(new Employee(C, Shenzhen,102));employees.add(new Employee(D, Chengdu,104));// group by CityMap employeesByCity employees.stream().collect( Collectors.groupingBy(Employee::getCity));// default void forEach(Consumer super T action) {for(Map.Entry entry:employeesByCity.entrySet()) {System.out.println(key entry.getKey() , Value entry.getValue());entry.getValue().forEach(System.out::println);}// 2016-01-15 20:37PMConsumer aa a - { System.out.println(Employee: a.getName() : a.getScore()); };List chengduEmployee employeesByCity.get(Chengdu);chengduEmployee.forEach(aa);// test for countingMap employeesByCity2 employees.stream().collect( Collectors.groupingBy(Employee::getCity, Collectors.counting()));printMap(employeesByCity2);// calculate average scoreMap employeesByCity3 employees.stream().collect( Collectors.groupingBy(Employee::getCity,Collectors.averagingInt(Employee::getScore)));printMap(employeesByCity3);/*Stream people Stream.of(new Person(Paul, 24), new Person(Mark, 30), new Person(Will, 28));Map peopleByAge people.collect(groupingBy(p - p.age, mapping((Person p) - p.name, toList())));System.out.println(peopleByAge);*//** 分区是一种特殊的分组结果 map 至少包含两个不同的分组——一个true一个false。* 例如如果想找出最优秀的员工你可以将所有雇员分为两组一组销售量大于 N* 另一组小于 N使用 partitioningBy 收集器*/System.out.println(partition result);Map partitioned employees.stream().collect(Collectors.partitioningBy(e - e.getScore() 101));printMap(partitioned);/** 你也可以将 groupingBy 收集器传递给 partitioningBy 收集器来将联合使用分区和分组。例如你可以统计每个分区中的每个城市的雇员人数Map result employees.stream().collect(partitioningBy(e - e.getNumSales() 150,groupingBy(Employee::getCity, counting())));这样会生成一个二级 Map:{false{London1}, true{New York1, Hong Kong1, London1}}*/}}要获取更多Jerry的原创文章请关注公众号汪子熙:
