Change DefaultSealable impl and add comments

VadereState/src/org/vadere/state/attributes/DefaultSealable.java

@@ -2,15 +2,32 @@ package org.vadere.state.attributes;
 
 import org.apache.commons.attributes.Sealable;
 
+/**
+ * Our implementation of {@link Sealable}.
+ * The {@code sealed} flag shall not be serialized.
+ * 
+ * @author Jakob Schöttl
+ *
+ */
 public class DefaultSealable implements Sealable {
 	
 	/** Should not be serialized. */
 	private transient boolean sealed;
 
+	/**
+	 * Apache Commons' DefaultSealable throws an exception if the object is already sealed.
+	 */
 	@Override
 	public void seal() {
-		if (sealed)
-			throw new IllegalStateException("Object is already sealed.");
+		// Attributes currently are sealed right before the simulation starts.
+		// Throwing an exception when they are already sealed makes a second simulation fail.
+		// Solutions (other than not throwing a exception) are:
+		// - Seal as soon as the objects are loaded from JSON.
+		// - Copy all attributes before starting a simulation.
+		//   This does not make sense, since the attributes are read-only anyway.
+
+//		if (sealed)
+//			throw new IllegalStateException("Object is already sealed.");
 		sealed = true;
 	}