싱글턴을 만드는 세가지 방법
public class Elvis {
public static final Elvis INSTANCE = new Elvis();
private Elvis() {...}
public void leaveTheBuilding() {...}
}
public class Elvis {
private static final Elvis INSTANCE = new Elvis();
private Elvis() {...}
public static Elvis getInstance() {return INSTANCE;}
public void leaveTheBuilding() {...}
}
public enum Elvis{
INSTANCE;
public void leaveTheBuilding() {...}
}