prmr#508 Built NotificationHandler class with basic singleton require…

…ments

src/org/jetuml/gui/NotificationHandler.java

@@ -0,0 +1,36 @@
+package org.jetuml.gui;
+
+import javafx.stage.Stage;
+
+import java.util.LinkedList;
+
+/**
+ * Singleton object that manages the notification object positions and display states.
+ */
+public final class NotificationHandler
+{
+
+    private static final NotificationHandler INSTANCE = new NotificationHandler();
+
+    private Stage aMainStage;
+    private LinkedList<Notification> aNotificationList = new LinkedList<>();
+
+    private NotificationHandler()
+    {}
+
+    /**
+     * @return The NotificationHandler singleton instance
+     */
+    public static NotificationHandler instance()
+    { return INSTANCE; }
+
+    /**
+     * Sets the parent stage of all the notification stages.
+     * @param pStage The target parent stage of the notification objects
+     */
+    public void setMainStage(Stage pStage)
+    {
+        this.aMainStage = pStage;
+    }
+
+}