可以使用Java 8中Stream API的Collectors.groupingBy()方法和Collectors.minBy()方法来实现按特性和该特性某个字段的最小值对收集器进行分组。假设有一个List
import java.util.*;
import java.util.stream.Collectors;
public class GroupByCharacteristicsExample {
public static void main(String[] args) {
List persons = Arrays.asList(
new Person("Alice", 18),
new Person("Bob", 22),
new Person("Charlie", 20),
new Person("Alice", 25),
new Person("Bob", 30),
new Person("Charlie", 27));
Map> minAges = persons.stream()
.collect(Collectors.groupingBy(
Person::getName,
Collectors.minBy(Comparator.comparingInt(Person::getAge)
)));
System.out.println(minAges);
}
}
class Person {
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}
输出结果为:
{Alice=Optional[Person{name='Alice', age=18}], Bob=Optional[Person{name='Bob', age=22}], Charlie=Optional[Person{name='Charlie', age=20}]}
其中,对persons进行了分组,并找到每个分组中年龄最小的那个Person对象。通过Collectors.groupingBy()方法对persons进行分组,按照Person对象的name属性进行分组,得到一个Map对象,其中key为name属性,value为经过Collect