[New] Added new ElementDateVisitor and ElementStateVisitor

These allow to get the date or state respectively from a
StrolchRootElement which supports such a field (Order and/or Activity)
and thus eliminates the need for casting

li.strolch.model/src/main/java/li/strolch/model/visitor/ElementDateVisitor.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2013 Robert von Burg <eitch@eitchnet.ch>
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package li.strolch.model.visitor;
+
+import java.util.Date;
+
+import li.strolch.model.Order;
+import li.strolch.model.Resource;
+import li.strolch.model.activity.Activity;
+
+/**
+ * @author Robert von Burg <eitch@eitchnet.ch>
+ */
+public class ElementDateVisitor implements StrolchRootElementVisitor<Date> {
+
+	@Override
+	public Date visitOrder(Order order) {
+		return order.getDate();
+	}
+
+	@Override
+	public Date visitResource(Resource resource) {
+		throw new IllegalArgumentException("Resources have no date!");
+	}
+
+	@Override
+	public Date visitActivity(Activity activity) {
+		throw new IllegalArgumentException("Activities have no date!");
+	}
+}

li.strolch.model/src/main/java/li/strolch/model/visitor/ElementStateVisitor.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2013 Robert von Burg <eitch@eitchnet.ch>
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package li.strolch.model.visitor;
+
+import li.strolch.model.Order;
+import li.strolch.model.Resource;
+import li.strolch.model.State;
+import li.strolch.model.activity.Activity;
+
+/**
+ * @author Robert von Burg <eitch@eitchnet.ch>
+ */
+public class ElementStateVisitor implements StrolchRootElementVisitor<State> {
+
+	@Override
+	public State visitOrder(Order order) {
+		return order.getState();
+	}
+
+	@Override
+	public State visitResource(Resource resource) {
+		throw new IllegalArgumentException("Resources have no state!");
+	}
+
+	@Override
+	public State visitActivity(Activity activity) {
+		return activity.getState();
+	}
+}