Stream操作流练习

基础数据：

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private String name;
    private int age;
    private String sex;
    private String city;
    private Integer money;
static   List<User> users = new ArrayList<>();

    public static void main(String[] args) {
        test1();
           
    }
 public static void test1(){

        users.add(new User("诺手",21,"男","北京",1200));
        users.add(new User("佛爷个",21,"男","北京",2100));
        users.add(new User("刀妹",23,"女","上海",3200));
        users.add(new User("海哥2",30,"女","上海",2600));
        users.add(new User("压缩",21,"男","苏州",2800));
        users.add(new User("马儿扎哈",21,"男","苏州",1500));
        users.add(new User("螳螂",30,"女","杭州",2560));
        users.add(new User("狮子狗",21,"男","杭州",2780));
        users.add(new User("赵信",21,"男","成都",1890));
    }
}

练习一：根据城市分组，代码如下：

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private String name;
    private int age;
    private String sex;
    private String city;
    private Integer money;
static   List<User> users = new ArrayList<>();

    public static void main(String[] args) {
        test1();
           test2{}
    }
 public static void test1(){

        users.add(new User("诺手",21,"男","北京",1200));
        users.add(new User("佛爷个",21,"男","北京",2100));
        users.add(new User("刀妹",23,"女","上海",3200));
        users.add(new User("海哥2",30,"女","上海",2600));
        users.add(new User("压缩",21,"男","苏州",2800));
        users.add(new User("马儿扎哈",21,"男","苏州",1500));
        users.add(new User("螳螂",30,"女","杭州",2560));
        users.add(new User("狮子狗",21,"男","杭州",2780));
        users.add(new User("赵信",21,"男","成都",1890));
    }
    //根据城市分组
    public static void test2(){
        Map<String,List<User>> collect=users.stream().collect(Collectors.groupingBy(User::getCity));
        collect.forEach((k,v)->{
            System.out.println("城市名:"+k);
            System.out.println(v);
        });
    }
}

运行结果如下：

练习二：列出每个城市的最有钱的

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private String name;
    private int age;
    private String sex;
    private String city;
    private Integer money;
static   List<User> users = new ArrayList<>();

    public static void main(String[] args) {
        test1();
          test4 () 
    }
 public static void test1(){

        users.add(new User("诺手",21,"男","北京",1200));
        users.add(new User("佛爷个",21,"男","北京",2100));
        users.add(new User("刀妹",23,"女","上海",3200));
        users.add(new User("海哥2",30,"女","上海",2600));
        users.add(new User("压缩",21,"男","苏州",2800));
        users.add(new User("马儿扎哈",21,"男","苏州",1500));
        users.add(new User("螳螂",30,"女","杭州",2560));
        users.add(new User("狮子狗",21,"男","杭州",2780));
        users.add(new User("赵信",21,"男","成都",1890));
    }
    //列出每个城市的最有钱的
    public static void test4(){
        Map<String, Optional<User>> collect=users.stream().collect(Collectors.groupingBy(User::getCity,Collectors.
                maxBy(Comparator.comparingInt(User::getMoney))));

        collect.forEach((k,v)->{
            System.out.println("地区："+k);
            System.out.println("冠军是："+v);
        });
    };
}

运行结果：

练习三根据性别分组：

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private String name;
    private int age;
    private String sex;
    private String city;
    private Integer money;
static   List<User> users = new ArrayList<>();

    public static void main(String[] args) {
        test1();
           test3()
    }
 public static void test1(){

        users.add(new User("诺手",21,"男","北京",1200));
        users.add(new User("佛爷个",21,"男","北京",2100));
        users.add(new User("刀妹",23,"女","上海",3200));
        users.add(new User("海哥2",30,"女","上海",2600));
        users.add(new User("压缩",21,"男","苏州",2800));
        users.add(new User("马儿扎哈",21,"男","苏州",1500));
        users.add(new User("螳螂",30,"女","杭州",2560));
        users.add(new User("狮子狗",21,"男","杭州",2780));
        users.add(new User("赵信",21,"男","成都",1890));
    }
    public static void test3(){
        Map<String,List<User>> collect=users.stream().collect(Collectors.groupingBy(User::getSex));
        collect.forEach((k,v)->{
            System.out.println("性别："+k);
            System.out.println(v);
        });
    }
}

结果如下

练习四：求每个城市的总金额

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private String name;
    private int age;
    private String sex;
    private String city;
    private Integer money;
  static   List<User> users = new ArrayList<>();
    public static void main(String[] args) {
        test1();
              test5();
    }
    public static void test1(){

        users.add(new User("京爷1",21,"男","北京",1200));
        users.add(new User("京爷2",21,"男","北京",2100));
        users.add(new User("海哥1",23,"女","上海",3200));
        users.add(new User("海哥2",30,"女","上海",2600));
        users.add(new User("苏姐1",21,"男","苏州",2800));
        users.add(new User("苏姐2",21,"男","苏州",1500));
        users.add(new User("螳螂",30,"女","杭州",2560));
        users.add(new User("狮子狗",21,"男","杭州",2780));
        users.add(new User("赵信",21,"男","成都",1890));
    }
    //求每个城市的销售总金额s
     public static void test5(){
        Map<String,Integer> map = users.stream().collect(Collectors.groupingBy(User::getCity,
                Collectors.summingInt(User::getMoney)));
       map.forEach((k,v)->{
           System.out.println("城市："+k);
           System.out.println("销售总额："+v);
       });
    }
}

结果

练习六；年龄大于28岁的

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private String name;
    private int age;
    private String sex;
    private String city;
    private Integer money;
  static   List<User> users = new ArrayList<>();
    public static void main(String[] args) {
        test1();
              test4();
    }
    public static void test1(){

        users.add(new User("京爷1",21,"男","北京",1200));
        users.add(new User("京爷2",21,"男","北京",2100));
        users.add(new User("海哥1",23,"女","上海",3200));
        users.add(new User("海哥2",30,"女","上海",2600));
        users.add(new User("苏姐1",21,"男","苏州",2800));
        users.add(new User("苏姐2",21,"男","苏州",1500));
        users.add(new User("螳螂",30,"女","杭州",2560));
        users.add(new User("狮子狗",21,"男","杭州",2780));
        users.add(new User("赵信",21,"男","成都",1890));
    }
  //过滤年领大于28的员工
  public static void test7(){
      List<User> collect = users.stream().filter(s -> s.getAge() > 28).collect(Collectors.toList());
      System.out.println(collect);
  }
}

结果如下：

练习八：根据moey给所有人排序

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private String name;
    private int age;
    private String sex;
    private String city;
    private Integer money;
  static   List<User> users = new ArrayList<>();
    public static void main(String[] args) {
        test1();
              test10();
    }
    public static void test1(){

        users.add(new User("京爷1",21,"男","北京",1200));
        users.add(new User("京爷2",21,"男","北京",2100));
        users.add(new User("海哥1",23,"女","上海",3200));
        users.add(new User("海哥2",30,"女","上海",2600));
        users.add(new User("苏姐1",21,"男","苏州",2800));
        users.add(new User("苏姐2",21,"男","苏州",1500));
        users.add(new User("螳螂",30,"女","杭州",2560));
        users.add(new User("狮子狗",21,"男","杭州",2780));
        users.add(new User("赵信",21,"男","成都",1890));
    }
    //全国根据销售金额排序
    public static void test10(){
         users.sort(Comparator.comparing(User::getMoney).reversed());
   int i=0;
   //遍历输出
    for(User user : users){
        i++;
        System.out.println("第"+i+"名:"+user);
    }
}

结果如下：

练习九，计算每人平均money

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private String name;
    private int age;
    private String sex;
    private String city;
    private Integer money;
  static   List<User> users = new ArrayList<>();
    public static void main(String[] args) {
        test1();
              test10();
    }
    public static void test1(){

        users.add(new User("京爷1",21,"男","北京",1200));
        users.add(new User("京爷2",21,"男","北京",2100));
        users.add(new User("海哥1",23,"女","上海",3200));
        users.add(new User("海哥2",30,"女","上海",2600));
        users.add(new User("苏姐1",21,"男","苏州",2800));
        users.add(new User("苏姐2",21,"男","苏州",1500));
        users.add(new User("螳螂",30,"女","杭州",2560));
        users.add(new User("狮子狗",21,"男","杭州",2780));
        users.add(new User("赵信",21,"男","成都",1890));
    }
   //人均销售金额
    public static void test9(){
        double asDouble = users.stream().mapToDouble(User::getMoney).average().getAsDouble();
        System.out.println(asDouble);
    }
}

练习十：总共有多少个不同的城市？

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private String name;
    private int age;
    private String sex;
    private String city;
    private Integer money;
  static   List<User> users = new ArrayList<>();
    public static void main(String[] args) {
        test1();
              test10();
    }
    public static void test1(){

        users.add(new User("京爷1",21,"男","北京",1200));
        users.add(new User("京爷2",21,"男","北京",2100));
        users.add(new User("海哥1",23,"女","上海",3200));
        users.add(new User("海哥2",30,"女","上海",2600));
        users.add(new User("苏姐1",21,"男","苏州",2800));
        users.add(new User("苏姐2",21,"男","苏州",1500));
        users.add(new User("螳螂",30,"女","杭州",2560));
        users.add(new User("狮子狗",21,"男","杭州",2780));
        users.add(new User("赵信",21,"男","成都",1890));
    }
    public static void testi(){
        List<String> collect = users.stream().map(User::getCity).distinct().collect(Collectors.toList());
        int size = collect.size();
        System.out.println("总共有"+size+"个城市，它们是："+collect);
    }
}

结果如下：