Stream practice

Stream 예제 실습

example domain class

import java.util.Objects;

public class OnlineClass {
    private Integer id;
    private String title;
    private boolean closed;

    public OnlineClass(Integer id, String title, boolean closed) {
        this.id = id;
        this.title = title;
        this.closed = closed;
    }

    public boolean titleStartsWith(String start) {
        return title.startsWith(start);
    }

    public boolean isClosed() {
        return closed;
    }

    public String title() {
        return title;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        OnlineClass that = (OnlineClass) o;
        return closed == that.closed && Objects.equals(id, that.id) && Objects.equals(title, that.title);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, title, closed);
    }

    @Override
    public String toString() {
        return "OnlineClass{" +
                "id=" + id +
                ", title='" + title + '\'' +
                ", closed=" + closed +
                '}';
    }
}

example App class

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class App {
    public static void main(String[] args) {
        List<OnlineClass> springClasses = new ArrayList<>();
        springClasses.add(new OnlineClass(1, "spring boot", true));
        springClasses.add(new OnlineClass(2, "spring data jpa", true));
        springClasses.add(new OnlineClass(3, "spring mvc", false));
        springClasses.add(new OnlineClass(4, "spring core", false));
        springClasses.add(new OnlineClass(5, "rest api development", false));

        System.out.println("\n::: spring 으로 시작하는 수업 :::");
        springClasses.stream()
                .filter(c -> c.titleStartsWith("spring"))
                .forEach(System.out::println);

        System.out.println("\n::: close 되지 않은 수업 :::");
        springClasses.stream()
                .filter(Predicate.not(OnlineClass::isClosed))
                .forEach(System.out::println);

        System.out.println("\n::: 수업 이름만 모아서 스트림 만들기 :::");
        springClasses.stream()
                .map(OnlineClass::title)
                .forEach(System.out::println);

        List<OnlineClass> javaClasses = new ArrayList<>();
        javaClasses.add(new OnlineClass(6, "The Java, Test", true));
        javaClasses.add(new OnlineClass(7, "The Java, Code manipulation", true));
        javaClasses.add(new OnlineClass(8, "The Java, 8 to 11", false));

        List<List<OnlineClass>> keesunEvents = new ArrayList<>();
        keesunEvents.add(springClasses);
        keesunEvents.add(javaClasses);

        System.out.println("\n::: 두 수업 목록에 들어있는 모든 수업 아이디 출력 :::");
        keesunEvents.stream()
                .flatMap(Collection::stream)
                .forEach(c -> System.out.println(c.id()));

        System.out.println("\n10부터 1씩 증가하는 무제한 스트림 중에서 앞에 10개 빼고 최대 10개 까지만");
        Stream.iterate(10, i -> i + 1)
                .skip(10)
                .limit(10)
                .forEach(System.out::println);

        System.out.println("\n자바 수업 중에 Test가 들어있는 수업이 있는지 확인");
        boolean test = javaClasses.stream()
                .anyMatch(c -> c.title().contains("Test"));
        System.out.println(test);

        System.out.println("\n스프링 수업 중에 제목에 spring이 들어간 것만 모아서 List로 만들기");
        List<OnlineClass> startsWithSpring = springClasses.stream()
                .filter(c -> c.titleStartsWith("spring"))
                .collect(Collectors.toList());
    }
}