in fact Java 1.5 should support enum in annotations if the enum is defined before the field declaration

sonar-check-api/src/main/java/org/sonar/check/Cardinality.java

@@ -1,27 +0,0 @@
-/*
- * Sonar, open source software quality management tool.
- * Copyright (C) 2009 SonarSource SA
- * mailto:contact AT sonarsource DOT com
- *
- * Sonar is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; either
- * version 3 of the License, or (at your option) any later version.
- *
- * Sonar is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with Sonar; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02
- */
-package org.sonar.check;
-
-/**
- * @since 2.3
- */
-public enum Cardinality {
-  SINGLE, MULTIPLE
-}

sonar-check-api/src/main/java/org/sonar/check/Rule.java

@@ -31,6 +31,11 @@ import java.lang.annotation.Target;
 @Target(ElementType.TYPE)
 public @interface Rule {
 
+  static enum Cardinality {
+    SINGLE, MULTIPLE
+  }
+
+
   /**
    * The default key is the class name.
    */