#354 added usergroup for version of feature toggle

feature-toggle/src/main/java/com/iluwatar/featuretoggle/user/User.java

@@ -0,0 +1,7 @@
+package com.iluwatar.featuretoggle.user;
+
+/**
+ * Created by joseph on 26/01/16.
+ */
+public class User {
+}

feature-toggle/src/main/java/com/iluwatar/featuretoggle/user/UserGroup.java

@@ -0,0 +1,37 @@
+package com.iluwatar.featuretoggle.user;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Created by joseph on 26/01/16.
+ */
+public class UserGroup {
+
+    private static List<User> freeGroup = new ArrayList<>();
+    private static List<User> paidGroup = new ArrayList<>();
+
+    public static void addUserToFreeGroup(final User user){
+        if(paidGroup.contains(user)){
+            throw new IllegalArgumentException("User all ready member of paid group.");
+        }else{
+            if(!freeGroup.contains(user)){
+                freeGroup.add(user);
+            }
+        }
+    }
+
+    public static void addUserToPaidGroup(final User user){
+        if(freeGroup.contains(user)){
+            throw new IllegalArgumentException("User all ready member of free group.");
+        }else{
+            if(!paidGroup.contains(user)){
+                paidGroup.add(user);
+            }
+        }
+    }
+
+    public static boolean isPaid(User user) {
+        return paidGroup.contains(user);
+    }
+}