- 상태에 특화된 행동들을 분리해 낼 수 있으며, 새로운 행동을 추가하더라도 다른 행동에 영 향을 주지 않는다
먼저 주어진 코드를 보자
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);
}
}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 + '\'' +
'}';
}
}public class Client {
public static void main(String[] args) {
Student student = new Student("saechimdaeki");
OnlineCourse onlineCourse = new OnlineCourse();
Student keesun = new Student("junseong");
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());
}
}특정한 상태마다 다르게 동작하는 오퍼레이션이 있는 위와 같은경우 상태패턴을 적용할 수 있다.
이제 패턴이 적용된 코드를 보자.
public interface State {
void addReview(String review, Student student);
void addStudent(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 + '\'' +
", onlineCourses=" + onlineCourses +
'}';
}
}@Getter
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 void changeState(State state) {
this.state=state;
}
}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);
}
}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 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 Client {
public static void main(String[] args) {
OnlineCourse onlineCourse=new OnlineCourse();
Student student=new Student("saechimdaeki");
Student junseong=new Student("junseong");
junseong.addPrivate(onlineCourse);
onlineCourse.addStudent(student);
onlineCourse.changeState(new Private(onlineCourse));
onlineCourse.addReview("hello",student);
System.out.println(onlineCourse.getState());
System.out.println(onlineCourse.getReviews());
System.out.println(onlineCourse.getStudents());
}
}