[State]상태 패턴

State Pattern

객체 내부 상태 변경에 따라 객체의 행동이 달라지는 패턴
상태에 특화된 행동들을 분리해 낼 수 있으며, 새로운 행동을 추가하더라도 다른 행동에 영향을 주지 않는다. 

 

BEFORE

Client

public class Client {

    public static void main(String[] args) {
        Student student = new Student("whiteship");
        OnlineCourse onlineCourse = new OnlineCourse();

        Student keesun = new Student("keesun");
        keesun.addPrivateCourse(onlineCourse);

        onlineCourse.addStudent(student);
        onlineCourse.changeState(OnlineCourse.State.PRIVATE);

        onlineCourse.addStudent(keesun);

        onlineCourse.addReview("hello", student);

        System.out.println(onlineCourse.getState());
        System.out.println(onlineCourse.getStudents());
        System.out.println(onlineCourse.getReviews());
    }
}

Student

public class Student {

    private String name;

    public Student(String name) {
        this.name = name;
    }

    private List<OnlineCourse> privateCourses = new ArrayList<>();

    public boolean isEnabledForPrivateClass(OnlineCourse onlineCourse) {
        return privateCourses.contains(onlineCourse);
    }

    public void addPrivateCourse(OnlineCourse onlineCourse) {
        this.privateCourses.add(onlineCourse);
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                '}';
    }
}

OnlineCourse

public class OnlineCourse {

    public enum State {
        DRAFT, PUBLISHED, PRIVATE
    }

    private State state = State.DRAFT;

    private List<String> reviews = new ArrayList<>();

    private List<Student> students = new ArrayList<>();

    public void addReview(String review, Student student) {
        if (this.state == State.PUBLISHED) {
            this.reviews.add(review);
        } else if (this.state == State.PRIVATE && this.students.contains(student)) {
            this.reviews.add(review);
        } else {
            throw new UnsupportedOperationException("리뷰를 작성할 수 없습니다.");
        }
    }

    public void addStudent(Student student) {
        if (this.state == State.DRAFT || this.state == State.PUBLISHED) {
            this.students.add(student);
        } else if (this.state == State.PRIVATE && availableTo(student)) {
            this.students.add(student);
        } else {
            throw new UnsupportedOperationException("학생을 해당 수업에 추가할 수 없습니다.");
        }

        if (this.students.size() > 1) {
            this.state = State.PRIVATE;
        }
    }

    public void changeState(State newState) {
        this.state = newState;
    }

    public State getState() {
        return state;
    }

    public List<String> getReviews() {
        return reviews;
    }

    public List<Student> getStudents() {
        return students;
    }

    private boolean availableTo(Student student) {
        return student.isEnabledForPrivateClass(this);
    }


}

 

 

AFTER

Client

public class Client {

    public static void main(String[] args) {
        OnlineCourse onlineCourse = new OnlineCourse();
        Student student = new Student("whiteship");
        Student keesun = new Student("keesun");
        keesun.addPrivate(onlineCourse);

        onlineCourse.addStudent(student);

        onlineCourse.changeState(new Private(onlineCourse));
        // 1명 이하 일때는 상태를 Private으로 먼저 변경해주거나,
        // 아래 학생 추가를 먼저 해주어서 Draft의 addStudent 로직안에서 
        // 상태를 Private으로 될 수 있도록 해주어야 리뷰 등록이 가능하다. 
        
        onlineCourse.addStudent(keesun);
        onlineCourse.addReview("hello", student);

        System.out.println(onlineCourse.getState());
        System.out.println(onlineCourse.getReviews());
        System.out.println(onlineCourse.getStudents());
    }
}

State - Draft, Private, Published

public interface State {

    void addReview(String review, Student student);

    void addStudent(Student student);
}


public class Draft implements State {

    private OnlineCourse onlineCourse;

    public Draft(OnlineCourse onlineCourse) {
        this.onlineCourse = onlineCourse;
    }

    @Override
    public void addReview(String review, Student student) {
        throw new UnsupportedOperationException("드래프트 상태에서는 리뷰를 남길 수 없습니다.");
    }

    @Override
    public void addStudent(Student student) {
        this.onlineCourse.getStudents().add(student);
        if (this.onlineCourse.getStudents().size() > 1) {
            this.onlineCourse.changeState(new Private(this.onlineCourse));
        }
    }
}


public class Private implements State {

    private OnlineCourse onlineCourse;

    public Private(OnlineCourse onlineCourse) {
        this.onlineCourse = onlineCourse;
    }

    @Override
    public void addReview(String review, Student student) {
        if (this.onlineCourse.getStudents().contains(student)) {
            this.onlineCourse.getReviews().add(review);
        } else {
            throw new UnsupportedOperationException("프라이빗 코스를 수강하는 학생만 리뷰를 남길 수 있습니다.");
        }
    }

    @Override
    public void addStudent(Student student) {
        if (student.isAvailable(this.onlineCourse)) {
            this.onlineCourse.getStudents().add(student);
        } else {
            throw new UnsupportedOperationException("프라이빗 코스를 수강할 수 없습니다.");
        }
    }
}


public class Published implements State {

    private OnlineCourse onlineCourse;

    public Published(OnlineCourse onlineCourse) {
        this.onlineCourse = onlineCourse;
    }

    @Override
    public void addReview(String review, Student student) {
        this.onlineCourse.getReviews().add(review);
    }

    @Override
    public void addStudent(Student student) {
        this.onlineCourse.getStudents().add(student);
    }
}

Student

public class Student {

    private String name;

    public Student(String name) {
        this.name = name;
    }

    private Set<OnlineCourse> onlineCourses = new HashSet<>();

    public boolean isAvailable(OnlineCourse onlineCourse) {
        return onlineCourses.contains(onlineCourse);
    }

    public void addPrivate(OnlineCourse onlineCourse) {
        this.onlineCourses.add(onlineCourse);
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                '}';
    }
}

OnlineCourser

public class OnlineCourse {

    private State state = new Draft(this);

    private List<Student> students = new ArrayList<>();

    private List<String> reviews = new ArrayList<>();

    public void addStudent(Student student) {
        this.state.addStudent(student);
    }

    public void addReview(String review, Student student) {
        this.state.addReview(review, student);
    }

    public State getState() {
        return state;
    }

    public List<Student> getStudents() {
        return students;
    }

    public List<String> getReviews() {
        return reviews;
    }

    public void changeState(State state) {
        this.state = state;
    }
}

 

 

[패턴 복습] 

장점	단점
- 상태에 따른 동작을 개별 클래스로 옮겨서 관리할 수 있다. - 기존의 특정 상태에 따른 동작을 변경하지 않고 새로운 상태에 다른 동작을 추가할 수 있다. - 코드 복잡도를 줄일 수 있다.	- 복잡도가 증가한다.