这篇文章主要介绍了JAVA8 STREAM COLLECT GROUPBY分组实例解析,文中通过示例代码介绍的非常详细，对大家的学习或者工作具有一定的参考学习价值,需要的朋友可以参考下
实体类People，有个返回list的buildPeopleList方法，方便测试。
import lombok.AllArgsConstructor;import lombok.Builder;import lombok.Data;import lombok.NoArgsConstructor;import java.util.ArrayList;import java.util.Arrays;import java.util.List;/** * @author: rhyme * @date: 2019-09-26 17:31 * @topic: "主题" * @description: "描述" */@Data@NoArgsConstructor@AllArgsConstructor@Builderpublic class People { private String name; private String character; private String sex; private int age; public static People buildDefault() { return People.builder().name("LuoTianyan").character("optimistic").sex("female").age(24).build(); } public static List<People> buildPeopleList() { People p1 = People.builder().name("LuoTianyan").character("optimistic").sex("female").age(24).build(); People p2 = People.builder().name("Zhang").character("optimistic").sex("female").age(23).build(); People p3 = People.builder().name("Hu").character("shy").sex("female").age(25).build(); People p4 = People.builder().name("Y").character("Righteous").sex("male").age(24).build(); return new ArrayList<>(Arrays.asList(p1, p2, p3, p4)); }}
测试类GroupByTest，分别根据性别分组，统计各个性别人数，以及各个性别映射姓名。
import org.junit.After;import org.junit.Before;import org.junit.Test;import org.springframework.util.CollectionUtils;import java.util.List;import java.util.Map;import java.util.function.BiConsumer;import java.util.stream.Collectors;/** * @author: rhyme * @date: 2019-10-14 15:59 * @topic: "主题" * @description: "描述" */public class GroupByTest { private List<People> people; private BiConsumer soutKV; private Map result; @Before public void init() { people = People.buildPeopleList(); soutKV = (k, v) -> System.out.println(k + ":" + v); } @After public void soutResult() { if (!CollectionUtils.isEmpty(result)) { result.forEach(soutKV); } } /** * 根据性别分组 */ @Test public void groupBySex() { result = people.stream().collect( Collectors.groupingBy(People::getSex) ); } /** * 分别统计不同性别各自的人数 */ @Test public void groupBySexCount() { result = people.stream().collect( Collectors.groupingBy(People::getSex, Collectors.counting() )); } /** * 分别统计不同性别各自的name列表 */ @Test public void groupBySexName() { result = people.stream().collect( Collectors.groupingBy( People::getSex, Collectors.mapping(People::getName, Collectors.toSet()) )); }}
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本文标题: JAVA8 STREAM COLLECT GROUPBY分组实例解析
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