Encapsulate Collection

메소드가 collection을 반환할 때
• 그 메소드가 읽기전용 view를 반환하게 수정하고 add() 와 delete() 메소드를 작성한다.

 

Before

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

public class EncapsulateCollection_before {

	static class Course {
		String name;
		boolean isAdvanced;

		public Course(String name, boolean isAdvanced) {
			this.name = name;
			this.isAdvanced = isAdvanced;
		};

		public boolean isAdvanced() {
			return this.isAdvanced;
		};
	}

	static class Person {
		private Set<Course> courses;

		// ...
		public Set<Course> getCourses() {
			return courses;
		}

		public void setCourses(Set arg) {
			courses = arg;
		}
	}

	public static void main(String[] args) {
		Person kent = new Person();
		Set<Course> s = new HashSet<Course>();
		s.add(new Course("Smalltalk Programming", false));
		s.add(new Course("Appreciating Single Malts", true));
		kent.setCourses(s);
		
		
		Course refact = new Course("Refactoring", true);
		kent.getCourses().add(refact);
		kent.getCourses().add(new Course("Brutal Sarcasm", false));
		
		kent.getCourses().remove(refact);

		Iterator<Course> iter = kent.getCourses().iterator();
		int count = 0;
		while (iter.hasNext()) {
			Course each = (Course) iter.next();
			if (each.isAdvanced())
				count++;
		}
		
		System.out.println("Advanced courses: " + count);
	}

}

 

After

public class ReplaceTypeCodeWithClass_before {
	static public class Person {
		private BloodGroup _bloodGroup;

		public int getBloodGroupCode(){
			return _bloodGroup.getCode();
		}

		public BloodGroup getBloodGroup(){
			return _bloodGroup;
		}

		public Person(BloodGroup bloodGroup){
			_bloodGroup = bloodGroup;
		}

		public void setBloodGroup(BloodGroup arg){
			_bloodGroup = arg;
		}
	}

	public static class BloodGroup{
		public static final BloodGroup O = new BloodGroup(0);
		public static final BloodGroup A = new BloodGroup(1);
		public static final BloodGroup B = new BloodGroup(2);
		public static final BloodGroup AB = new BloodGroup(3);

		private static final BloodGroup[] _values = {O, A, B, AB};
		private final int _code;

		private BloodGroup(int code){
			_code = code;
		}
		public int getCode(){
			return _code;
		}
		public static BloodGroup code(int arg){
			return _values[arg];
		}
	}
	
	public static void main(String[] args) {

		Person thePerson = new Person(BloodGroup.A);
		System.out.println("Blood group : " + thePerson.getBloodGroup());

		thePerson.setBloodGroup(BloodGroup.AB);
		System.out.println("Blood group : " + thePerson.getBloodGroup());
	}

}