java使用Stream流找出集合对象中最小值_stream获取最小值

一、问题

有如下四个人，如何使用Lamdba找到年龄最小的并打印出来

@Data
@AllArgsConstructor
@NoArgsConstructor
@EqualsAndHashCode
public class Person {
    private String name;
    private  Integer age;
}

  List<Person> persons = Stream.of(new Person("老王", 35)
                , new Person("老张", 23)
                , new Person("老周", 56)
                , new Person("老李", 48))
                .collect(Collectors.toList());

 二、使用sorted+limit

       persons.stream()
                .sorted((p1, p2) -> p2.getAge() - p1.getAge())
                .limit(1).forEach((person) -> {
            System.out.println("sorted+limit:" + JSON.toJSONString(person));
            //   sorted+limit:{"age":56,"name":"老周"}
        });

三、使用 sorted+skip(不推荐)

     persons.stream()
                .sorted((p1, p2) -> p1.getAge() - p2.getAge())
                .skip(persons.size() - 1).forEach((person) -> {
            System.out.println("sorted+skip:" + JSON.toJSONString(person));
            //      sorted+skip:{"age":56,"name":"老周"}
        });

 四、使用max

        Optional<Person> max = persons.stream()
                .max((p1, p2) -> p1.getAge() - p2.getAge());
        max.ifPresent((person -> {
            System.out.println("max:" + JSON.toJSONString(person));
            //   max:{"age":56,"name":"老周"}
        }));

五、使用min（不推荐）

   Optional<Person> min = persons.stream()
                .min((p1, p2) -> p2.getAge() - p1.getAge());
        min.ifPresent((person -> {
            System.out.println("min:" + JSON.toJSONString(person));
            //    min:{"age":56,"name":"老周"}
        }));

六、使用reduce（推荐）

    Optional<Person> cacl2 = persons.stream()
                .reduce((p1, p2) -> p1.getAge() > p2.getAge() ? p1 : p2);
        cacl2.ifPresent(person -> {
            System.out.println("reduce" + JSON.toJSONString(person));
            //   reduce{"age":56,"name":"老周"}
        });

七、完整代码及结果

 private static void test01() {
        List<Person> persons = Stream.of(new Person("老王", 35)
                , new Person("老张", 23)
                , new Person("老周", 56)
                , new Person("老李", 48))
                .collect(Collectors.toList());
        System.out.println(JSON.toJSONString(persons));
        //[{"age":35,"name":"老王"},{"age":23,"name":"老张"},{"age":56,"name":"老周"},{"age":48,"name":"老例"}]
 
        //    找出年龄最大的人，并输入姓名和年龄
 
        persons.stream()
                .sorted((p1, p2) -> p2.getAge() - p1.getAge())
                .limit(1).forEach((person) -> {
            System.out.println("sorted+limit:" + JSON.toJSONString(person));
            //   sorted+limit:{"age":56,"name":"老周"}
        });
 
        persons.stream()
                .sorted((p1, p2) -> p1.getAge() - p2.getAge())
                .skip(persons.size() - 1).forEach((person) -> {
            System.out.println("sorted+skip:" + JSON.toJSONString(person));
            //      sorted+skip:{"age":56,"name":"老周"}
        });
 
        Optional<Person> max = persons.stream()
                .max((p1, p2) -> p1.getAge() - p2.getAge());
        max.ifPresent((person -> {
            System.out.println("max:" + JSON.toJSONString(person));
            //   max:{"age":56,"name":"老周"}
        }));
 
        Optional<Person> min = persons.stream()
                .min((p1, p2) -> p2.getAge() - p1.getAge());
        min.ifPresent((person -> {
            System.out.println("min:" + JSON.toJSONString(person));
            //    min:{"age":56,"name":"老周"}
        }));
 
 
 
        Optional<Person> cacl2 = persons.stream()
                .reduce((p1, p2) -> p1.getAge() > p2.getAge() ? p1 : p2);
        cacl2.ifPresent(person -> {
            System.out.println("reduce" + JSON.toJSONString(person));
            //   reduce{"age":56,"name":"老周"}
        });
 
    }

[{"age":35,"name":"老王"},{"age":23,"name":"老张"},{"age":56,"name":"老周"},{"age":48,"name":"老李"}]
sorted+limit:{"age":56,"name":"老周"}
sorted+skip:{"age":56,"name":"老周"}
max:{"age":56,"name":"老周"}
min:{"age":56,"name":"老周"}
reduce{"age":56,"name":"老周"}