Implement Undo feature (#2).

Also refactored the direction heading from an int to a enum.

Convertor/src/turtle/editor/TMXToMTP.java

@@ -192,6 +192,16 @@ public static void main(String[] args) throws Exception
 			return;
 		if (!file.contains("."))
 			file += ".mtp";
+
+		try
+        {
+            LevelPack prev = new LevelPack(new File(file));
+            pck.setLevelPackID(prev.getLevelPackID());
+        }
+        catch (Exception e)
+        {
+            //Does nothing
+        }
 		pck.savePack(new File(file));
 	}
 
@@ -357,6 +367,18 @@ private static Object parseValue(String loc, String prop, String val)
 							"short property: '" + prop + "' --> '" + val + "'");
 					return null;
 				}
+			case "direction":
+				try
+				{
+					int num = Integer.parseInt(parts[1]);
+					return Direction.values()[num];
+				}
+				catch (Exception e)
+				{
+					System.err.println("WARNING: " + loc + " has an invalid " +
+							"direction property: '" + prop + "' --> '" + val + "'");
+					return null;
+				}
 			case "int":
 				try
 				{

src/turtle/attributes/Attributable.java

@@ -1,21 +1,47 @@
 package turtle.attributes;
 
+import java.io.Serializable;
+
 /**
  * This interface encompasses any object that contains a set of attributes that can be set.
  *
  * @author Henry
  *
  */
-public interface Attributable {
+public interface Attributable extends Serializable
+{
 
+	/**
+	 * Gets the value of a particular attribute.
+	 *
+	 * @param name the name of the attribute.
+	 * @return the value (or null if attribute does not exist)
+	 * @see AttributeSet#getAttribute(String)
+	 */
 	default Object getAttribute(String name) {
 		return getAttributeSet().getAttribute(name);
 	}
 
+	/**
+	 * Gets the value of a particular attribute.
+	 *
+	 * @param name the name of the attribute.
+	 * @param def  the default value to return.
+	 * @return the value.
+	 * @see AttributeSet#getAttribute(String, Object)
+	 */
 	default Object getAttribute(String name, Object def) {
 		return getAttributeSet().getAttribute(name, def);
 	}
 
+	/**
+	 * Sets the value of a particular attribute.
+	 *
+	 * @param name the name of the attribute.
+	 * @param value the value to set.
+	 * @throws IllegalArgumentException if value cannot cast into attribute type
+	 * @see AttributeSet#setAttribute(String, Object)
+	 */
 	default void setAttribute(String name, Object value) {
 		getAttributeSet().setAttribute(name, value);
 	}

src/turtle/attributes/Attribute.java

@@ -8,6 +8,8 @@
  * Attribute.java
  *
  * Holds the getters/setters of a particular attribute.
+ *
+ * @author Henry Wang
  */
 public class Attribute
 {

src/turtle/attributes/AttributeSet.java

@@ -1,5 +1,8 @@
 package turtle.attributes;
 
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.Serializable;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
 import java.util.*;
@@ -13,7 +16,7 @@
  * @author Henry
  * @see turtle.attributes.Attributable
  */
-public class AttributeSet<A extends Attributable>
+public class AttributeSet<A extends Attributable> implements Serializable
 {
 
     @SuppressWarnings("unused")
@@ -23,7 +26,8 @@ public class AttributeSet<A extends Attributable>
     private static final String SET_PREFIX = "set";
     private static final HashMap<Class<?>, Attribute[]> attributeCache = new
             HashMap<>();
-    private final Hashtable<String, Attribute> attrs = new Hashtable<>();
+
+    private transient Hashtable<String, Attribute> attrs;
     private final A attributable;
 
     /**
@@ -33,6 +37,7 @@ public class AttributeSet<A extends Attributable>
     public AttributeSet(A obj)
     {
         attributable = obj;
+        attrs = new Hashtable<>();
         if (!attributeCache.containsKey(obj.getClass()))
             extractAttributes(attributable);
         for (Attribute attr : attributeCache.get(obj.getClass()))
@@ -271,4 +276,22 @@ public void setAttribute(String name, Object value)
         attr.set(attributable, value);
     }
 
+    /**
+     * Reads this object from the provided input stream.
+     *
+     * @param in the input stream to read from
+     * @throws IOException if an I/O error occurs
+     * @throws ClassNotFoundException if a class cannot be found.
+     */
+    private void readObject(ObjectInputStream in)
+         throws IOException, ClassNotFoundException
+    {
+        in.defaultReadObject();
+        attrs = new Hashtable<>();
+        Attributable obj = getAttributable();
+        if (!attributeCache.containsKey(obj.getClass()))
+            extractAttributes(attributable);
+        for (Attribute attr : attributeCache.get(obj.getClass()))
+            attrs.put(attr.getName(), attr);
+    }
 }

src/turtle/attributes/NotAttribute.java

@@ -10,6 +10,7 @@
  * NotAttribute.java
  *
  * This annotation remarks that a particular method is not an attribute.
+ * @author Henry
  */
 @Documented
 @Retention(value = RetentionPolicy.RUNTIME)

src/turtle/comp/Bird.java

@@ -1,5 +1,6 @@
 package turtle.comp;
 
+import turtle.core.Direction;
 import turtle.core.Location;
 
 /**
@@ -14,22 +15,12 @@
  */
 public class Bird extends Enemy
 {
-    /**
-     * The default image for this component
-     */
     public static final int DEFAULT_IMAGE = 52;
-
-    private static final int BIRD_STILL_IMAGE = 52;
+    private static final int BIRD_STILL_IMAGE = DEFAULT_IMAGE;
     private static final int BIRD_FLYING_IMAGE = 53;
 
+    private static final long serialVersionUID = -387220900586289450L;
 
-    /**
-     * Creates a new bird and initializes image.
-     */
-    public Bird()
-    {
-        setImageFrame(BIRD_STILL_IMAGE);
-    }
 
     /**
      * Updates frames so that the bird will change between flying/ still
@@ -47,9 +38,9 @@ public void updateFrame(long frame)
             Player p = getParentGrid().getPlayer();
             if (p != null)
             {
-                int[] movement = calculateDirection();
+                Direction[] movement = calculateDirection();
                 boolean moved = false;
-                for (int dir : movement)
+                for (Direction dir : movement)
                 {
                     if (traverseDirection(dir))
                     {
@@ -62,7 +53,7 @@ public void updateFrame(long frame)
                 if (!moved)
                 {
                     setImageFrame(BIRD_STILL_IMAGE);
-                    setHeading(NORTH);
+                    setHeading(Direction.NORTH);
                 }
             }
         }
@@ -74,45 +65,45 @@ public void updateFrame(long frame)
      *
      * @return a list of possible directions to move into.
      */
-    private int[] calculateDirection()
+    private Direction[] calculateDirection()
     {
         Player player = getParentGrid().getPlayer();
         if (player == null)
-            return new int[0];
+            return new Direction[0];
 
         Location playerLoc = player.getHeadLocation();
         Location loc = getHeadLocation();
         if (!playerLoc.isValidLocation() || !loc.isValidLocation())
-            return new int[0];
+            return new Direction[0];
 
         int dr = playerLoc.getRow() - loc.getRow();
         int dc = playerLoc.getColumn() - loc.getColumn();
 
-        int rowDir = -1;
-        int colDir = -1;
+        Direction rowDir = null;
+        Direction colDir = null;
 
         if (dr < 0)
-            rowDir = NORTH;
+            rowDir = Direction.NORTH;
         else if (dr > 0)
-            rowDir = SOUTH;
+            rowDir = Direction.SOUTH;
 
         if (dc < 0)
-            colDir = WEST;
+            colDir = Direction.WEST;
         else if (dc > 0)
-            colDir = EAST;
+            colDir = Direction.EAST;
 
-        if (rowDir == -1 && colDir == -1)
-            return new int[0];
+        if (rowDir == null && colDir == null)
+            return new Direction[0];
 
-        if (rowDir == -1)
-            return new int[]{colDir};
-        if (colDir == -1)
-            return new int[]{rowDir};
+        if (rowDir == null)
+            return new Direction[]{colDir};
+        if (colDir == null)
+            return new Direction[]{rowDir};
 
         if (Math.abs(dr) > Math.abs(dc))
         {
-            return new int[]{rowDir, colDir};
+            return new Direction[]{rowDir, colDir};
         } else
-            return new int[]{colDir, rowDir};
+            return new Direction[]{colDir, rowDir};
     }
 }