[refactor] Update StarType enum in memento pattern.

memento/src/main/java/com/iluwatar/StarType.java

@@ -2,31 +2,16 @@ package com.iluwatar;
 
 public enum StarType {
 
-	SUN, RED_GIANT, WHITE_DWARF, SUPERNOVA, DEAD;
+	SUN("sun"), RED_GIANT("red giant"), WHITE_DWARF("white dwarf"), SUPERNOVA("supernova"), DEAD("dead star"), UNDEFINED("");
 
-	@Override
+    private String title;
+
+    StarType(String title) {
+        this.title = title;
+    }
+
+    @Override
 	public String toString() {
-		String s = "";
-		switch (this) {
-		case RED_GIANT:
-			s = "red giant";
-			break;
-		case SUN:
-			s = "sun";
-			break;
-		case SUPERNOVA:
-			s = "supernova";
-			break;
-		case WHITE_DWARF:
-			s = "white dwarf";
-			break;
-		case DEAD:
-			s = "dead star";
-			break;
-		default:
-			break;
-		}
-		return s;
+		return title;
 	}
-
 }