目标

操作数据

相关依赖

中间方法

distinct

filter

map

flatMap

limit

skip

sorted

终止方法

allMatch

anyMatch

collect

findAny

findFirst

forEach

max/min

noneMatch

reduce

Collectors的方法

averaging

collectingAndThen

countIng

groupingBy

joining

mapping

maxBy/minBy

partitioningBy

summarizing

项目下载地址

目标

熟练使用stream操作集合，能通过例题举一反三，合理地将案例融入到实际工作中。

操作数据

package com.stream.data.bean;

import lombok.Data;

@Data
public class Student {
    private String name;
    private int age;
    private boolean sex;
    //语文分数
    private float chineseScore;
    //数学分数
    private float mathScore;

    public Student(String name,int age,boolean sex,float chineseScore,float mathScore){
        this.name=name;
        this.age=age;
        this.sex=sex;
        this.chineseScore=chineseScore;
        this.mathScore=mathScore;
    }
    public Student(String name,int age,boolean sex){
        this.name=name;
        this.age=age;
        this.sex=sex;
    }
    public Student(int age){
        this.age=age;
    };

}

package com.stream.data;

import com.stream.data.bean.Student;

import java.util.*;

public class StreamData {
    //姓名集合
    public static List nameList;
    public static List animalList;
    public static List studentInfoList;
    public static List numList;
    public static List numContainNullList;
    public static List numAllNullList;
    public static List numDoubleList;
    public static List fingerGuessingList;
    public static List> studentAchievementList=new ArrayList<>();
    public static String[] nameArr;
    public static Map map=new HashMap<>();
    static {
        map.put("className","123班");
        map.put("classNo","123");
        map.put("stuNo","123456");
        map.put("stuName","张三");
        map.put("courseNo","Chinese");
        map.put("courseName","语文");
        map.put("grade",98.9);
        animalList=Arrays.asList("猫","狗","鸡","鸭");
        nameArr=new String[]{"阿里巴巴","腾讯","字节跳动","爱奇艺"};
        fingerGuessingList=Arrays.asList("石头","剪刀","布");
        nameList = Arrays.asList("张三", null, null, "李四", "李四", "王五", "张三丰", "李明", "陈小东", "小张");
        studentInfoList = Arrays.asList(
                new Student("张三", 12, true),
                new Student("李四", 13, true),
                new Student("王五", 12, false),
                new Student("赵六", 14, true),
                new Student("钱七", 12, false),
                new Student("钱七", 16, false),
                new Student("钱七", 16, false),
                new Student(null, 16, false),
                new Student("", 19, false),
                new Student(null, 16, false)
        );
        numDoubleList = Arrays.asList(1.4, 2.7, 35.4, 6.5, 22.0, 8.2, 3.3, 0.4, 48.9);
        numList = Arrays.asList(1, 2, 3, 6, 22, 8, 3, 0, 48);
        numContainNullList = Arrays.asList(1, null, -3, 6, 22, -8, 3, 0, 48);
        numAllNullList=Arrays.asList(null,null);
        Map studentAchievementMap = new HashMap<>();
        studentAchievementMap.put("className","123班");
        studentAchievementMap.put("classNo","123");
        studentAchievementMap.put("stuNo","123456");
        studentAchievementMap.put("stuName","张三");
        studentAchievementMap.put("courseNo","Chinese");
        studentAchievementMap.put("courseName","语文");
        studentAchievementMap.put("grade",98.9);
        Map studentAchievementMap1 = new HashMap<>();
        studentAchievementMap1.put("className","123班");
        studentAchievementMap1.put("classNo","123");
        studentAchievementMap1.put("stuNo","123456");
        studentAchievementMap1.put("stuName","张三");
        studentAchievementMap1.put("courseNo","Math");
        studentAchievementMap1.put("courseName","数学");
        studentAchievementMap1.put("grade",91.1);
        Map studentAchievementMap2 = new HashMap<>();
        studentAchievementMap2.put("className","123班");
        studentAchievementMap2.put("classNo","123");
        studentAchievementMap2.put("stuNo","123456");
        studentAchievementMap2.put("stuName","张三");
        studentAchievementMap2.put("courseNo","English");
        studentAchievementMap2.put("courseName","英语");
        studentAchievementMap2.put("grade",92.0);

        Map studentAchievementMap3 = new HashMap<>();
        studentAchievementMap3.put("className","123班");
        studentAchievementMap3.put("classNo","123");
        studentAchievementMap3.put("stuNo","123457");
        studentAchievementMap3.put("stuName","李四");
        studentAchievementMap3.put("courseNo","Chinese");
        studentAchievementMap3.put("courseName","语文");
        studentAchievementMap3.put("grade",100);
        Map studentAchievementMap4 = new HashMap<>();
        studentAchievementMap4.put("className","123班");
        studentAchievementMap4.put("classNo","123");
        studentAchievementMap4.put("stuNo","123457");
        studentAchievementMap4.put("stuName","李四");
        studentAchievementMap4.put("courseNo","Math");
        studentAchievementMap4.put("courseName","数学");
        studentAchievementMap4.put("grade",98.5);
        Map studentAchievementMap5 = new HashMap<>();
        studentAchievementMap5.put("className","123班");
        studentAchievementMap5.put("classNo","123");
        studentAchievementMap5.put("stuNo","123457");
        studentAchievementMap5.put("stuName","李四");
        studentAchievementMap5.put("courseNo","English");
        studentAchievementMap5.put("courseName","英语");
        studentAchievementMap5.put("grade",89.0);


        Map studentAchievementMap6 = new HashMap<>();
        studentAchievementMap6.put("className","124班");
        studentAchievementMap6.put("classNo","124");
        studentAchievementMap6.put("stuNo","123458");
        studentAchievementMap6.put("stuName","王五");
        studentAchievementMap6.put("courseNo","Chinese");
        studentAchievementMap6.put("courseName","语文");
        studentAchievementMap6.put("grade",88.5);
        Map studentAchievementMap7 = new HashMap<>();
        studentAchievementMap7.put("className","124班");
        studentAchievementMap7.put("classNo","124");
        studentAchievementMap7.put("stuNo","123458");
        studentAchievementMap7.put("stuName","王五");
        studentAchievementMap7.put("courseNo","Math");
        studentAchievementMap7.put("courseName","数学");
        studentAchievementMap7.put("grade",90.0);
        Map studentAchievementMap8 = new HashMap<>();
        studentAchievementMap8.put("className","124班");
        studentAchievementMap8.put("classNo","124");
        studentAchievementMap8.put("stuNo","123458");
        studentAchievementMap8.put("stuName","王五");
        studentAchievementMap8.put("courseNo","English");
        studentAchievementMap8.put("courseName","英语");
        studentAchievementMap8.put("grade",95.0);

        Map studentAchievementMap9 = new HashMap<>();
        studentAchievementMap9.put("className","124班");
        studentAchievementMap9.put("classNo","124");
        studentAchievementMap9.put("stuNo","123459");
        studentAchievementMap9.put("stuName","赵六");
        studentAchievementMap9.put("courseNo","Chinese");
        studentAchievementMap9.put("courseName","语文");
        studentAchievementMap9.put("grade",99.5);
        Map studentAchievementMap10 = new HashMap<>();
        studentAchievementMap10.put("className","124班");
        studentAchievementMap10.put("classNo","124");
        studentAchievementMap10.put("stuNo","123459");
        studentAchievementMap10.put("stuName","赵六");
        studentAchievementMap10.put("courseNo","Math");
        studentAchievementMap10.put("courseName","数学");
        studentAchievementMap10.put("grade",81.5);
        Map studentAchievementMap11 = new HashMap<>();
        studentAchievementMap11.put("className","124班");
        studentAchievementMap11.put("classNo","124");
        studentAchievementMap11.put("stuNo","123459");
        studentAchievementMap11.put("stuName","赵六");
        studentAchievementMap11.put("courseNo","English");
        studentAchievementMap11.put("courseName","英语");
        studentAchievementMap11.put("grade",80.0);

        studentAchievementList.add(studentAchievementMap);
        studentAchievementList.add(studentAchievementMap1);
        studentAchievementList.add(studentAchievementMap2);
        studentAchievementList.add(studentAchievementMap3);
        studentAchievementList.add(studentAchievementMap4);
        studentAchievementList.add(studentAchievementMap5);
        studentAchievementList.add(studentAchievementMap6);
        studentAchievementList.add(studentAchievementMap7);
        studentAchievementList.add(studentAchievementMap8);
        studentAchievementList.add(studentAchievementMap9);
        studentAchievementList.add(studentAchievementMap10);
        studentAchievementList.add(studentAchievementMap11);
    }
}

中间方法

distinct

作用：过滤重复数据。

需求一：过滤集合中重复的姓名。

方案：

    public static void distinctName() {
        List nameList = StreamData.nameList;
        System.out.println("原来的集合："+nameList);
        List list = nameList.stream().distinct().collect(
                Collectors.toList()
        );
        System.out.println("现在的集合："+list);
    }

返回结果：

原来的集合：[张三, null, null, 李四, 李四, 王五, 张三丰, 李明, 陈小东, 小张]
现在的集合：[张三, null, 李四, 王五, 张三丰, 李明, 陈小东, 小张]

需求二：根据姓名，过滤掉重复的数据。

方案：

    public static  Predicate distinct(Function keyExtractor) {
        Set

JDK8的新特性stream——让数据结构更具艺术性

中间方法

终止方法

Collectors的方法

Java相关栏目本月热门文章