Collector

import java.util.*;
import java.util.function.Supplier;
import java.util.stream.Collector;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Example {
    public static void main(String[] args) {
        List<Student> totalList = Arrays.asList(new Student("홍길동", 10, Student.Sex.MALE),
                new Student("김수애", 6, Student.Sex.FEMALE),
                new Student("신용권", 10, Student.Sex.MALE),
                new Student("박수미", 6, Student.Sex.FEMALE));




        //남학생들만 묶어서 List 생성
       /*
        Stream<Student> totalStream=totalList.stream();
        Stream<Student>maleStream=totalStream.filter(s->s.getSex()== Student.Sex.MALE);
        Collector<Student,?,List<Student>>collector=Collectors.toList();//리스트에서 student를 수집하는 collector를 얻는다.
        List<Student>maleList=maleStream.collect(collector);
        */
        // 변수 생략하고 간단하게
        List<Student>maleList=totalList.stream().filter(s->s.getSex()== Student.Sex.MALE).collect(Collectors.toList());
        maleList.stream().forEach(s->System.out.println(s.getName()));

        //여학생들만 필터링해서 별도의 HashSet
        /*
        Stream<Student>totalStream=totalList.stream();
        Stream<Student>femaleStream=totalStream.filter(s->s.getSex()== Student.Sex.FEMALE);
        Supplier<HashSet<Student>> supplier = HashSet::new; //새로운 hashset을 공급하는 supplier얻기
        Collector<Student,?,HashSet<Student>> collector=Collectors.toCollection(supplier);//suppier가 공급하는 hashset에 student를 수집하는 collector생성
        Set<Student>femaleSet=femaleStream.collect(collector); //stream에서 collect 메소드로 student 를 수집해서 hashset을 얻는다
        */
        Set<Student>femaleSet=totalList.stream().filter(s->s.getSex()== Student.Sex.FEMALE).collect(Collectors.toCollection(HashSet::new));

    }
}

public class Student {
    public enum Sex {MALE, FEMALE}

    public enum City {Seoul, Pusan}

    private String name;
    private int score;
    private Sex sex;
    private City city;

    public Student(String name, int score, Sex sex) {
        this.name = name;
        this.score = score;
        this.sex = sex;
    }

    public Student(String name, int score, Sex sex, City city) {
        this(name, score, sex);
        this.city = city;
    }

    public String getName() {
        return name;
    }

    public City getCity() {
        return city;
    }

    public Sex getSex() {
        return sex;
    }

    public int getScore() {
        return score;
    }
}