Enum

JDK 1.5에 추가된 기능.

enum Direction { EAST, WEST, ...}

열거형에 멤버 추가

열거형 상수의 이름 옆에 원하는 값을 괄호와 함꼐 적어주면 된다.

enum Direction {
	EAST(1), SOUTH(5), WEST(-1), NORTH(10);

	private final int value;

	Direction(int value) {
		this.value = value;
	}

	public int getValue() {
		return value;
	}
}

열거형에 추상 메소드 추가하기

열거형에 추상 메서드를 선언하면 각 열거형 상수가 이 추상 메서드를 반드시 구현해야 한다. 필드값을 protected로 해야 메소드에서 각 상수에 접근이 가능하다.

enum Direction {
	EAST(1) {
		@Override
		int cost(int distance) {
			return distance * value;
		}
	},
	SOUTH(5) {
		@Override
		int cost(int distance) {
			return distance * value;
		}
	},
	WEST(-1) {
		@Override
		int cost(int distance) {
			return distance * value;
		}
	},
	NORTH(10) {
		@Override
		int cost(int distance) {
			return distance * value;
		}
	};

	abstract int cost(int distance);

	protected final int value;
	
	Direction(int value) {
		this.value = value;
	}

	public int getValue() {
		return value;
	}
}

열거형의 이해

내부적인 열거형의 구현

class Direction {

	public static void main(String[] args) {
		System.out.println(Direction.EAST.getName());
	}
	
	
	static final Direction EAST = new Direction("EAST");
	static final Direction SOUTH = new Direction("SOUTH");
	static final Direction WEST = new Direction("WEST");
	static final Direction NORTH = new Direction("NORTH");
	
	private String name;
	
	
	
	private Direction(String name) {
		this.name = name;
	}

	public String getName() {
		return name;
	}
}

abstract class MyEnum<T extends  MyEnum<T>> implements Comparable<T>{
	static int id = 0;
	int oridinal;
	String name = "";

	public int oridinal(){ return oridinal; }

	MyEnum(String name){
		this.name = name;
		oridinal = id++;
	}

	public int compareTo(T t){
		return oridinal - t.oridinal();
	}
}

abstract class MyTransportation extends MyEnum {
	static final MyTransportation BUS = new MyTransportation("BUS", 100) {
		int fare(int distance) { return distance - BASIC_FARE; }
	};
	static final MyTransportation TRAIN = new MyTransportation("TRAIN", 150) {
		int fare(int distance) { return distance - BASIC_FARE; }
	};
	static final MyTransportation SHIP = new MyTransportation("SHIP", 100) {
		int fare(int distance) { return distance - BASIC_FARE; }
	};
	static final MyTransportation AIRPLANE = new MyTransportation("AIRPLANE", 300) {
		int fare(int distance) { return distance - BASIC_FARE; }
	};

	abstract int fare(int distance); // 거리에 따른 요금을 계산하는 추상 메서드
	protected final int BASIC_FARE; // protected로 해야 각 상수에서 접근 가능
	private MyTransportation(String name, int basicFare){
		super(name);
		BASIC_FARE = basicFare;
	}

	public String name() { return name; }
	public String toString() { return name; }

}

public class EnumEx4 {
	public static void main(String[] args) {
		MyTransportation t1 = MyTransportation.BUS;
		MyTransportation t2 = MyTransportation.BUS;
		MyTransportation t3 = MyTransportation.SHIP;
		MyTransportation t4 = MyTransportation.AIRPLANE;
		MyTransportation t5 = MyTransportation.AIRPLANE;

		System.out.printf("t1=%s, %d%n", t1.name(), t1.oridinal());
		System.out.printf("t2=%s, %d%n", t2.name(), t2.oridinal());
		System.out.printf("t3=%s, %d%n", t3.name(), t3.oridinal());
		System.out.printf("t4=%s, %d%n", t4.name(), t4.oridinal());
		System.out.printf("t5=%s, %d%n", t5.name(), t5.oridinal());
		System.out.println("t1==t2 ? "+ (t1==t2));
		System.out.println("t1.compareTo(t3)="+ t1.compareTo(t3));
	}
}

// 결과 :
t1=BUS, 0
t2=BUS, 0
t3=SHIP, 2
t4=AIRPLANE, 3
t5=AIRPLANE, 3
t1==t2 ? true
t1.compareTo(t3)=-2