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spublic 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：

练习本章代码需要额外的lombok包依赖文件，加载到pomwen文件中

<dependency>

<groupId>org.projectlombok</groupId>

<artifactId>lombok</artifactId>

<optional>true</optional>

<version>1.18.24</version>

</dependency>