Add @unsigned annotation.

Author: greenrobot-team

objectbox-java-api/src/main/java/io/objectbox/annotation/Unsigned.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2019 ObjectBox Ltd. All rights reserved.
+ *
+ * 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 io.objectbox.annotation;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Indicates that values of an integer property (e.g. int and long in Java)
+ * should be treated as unsigned when doing queries or creating indexes.
+ * <p>
+ * For example consider a set of integers sorted by the default order: [-2, -1, 0, 1, 2].
+ * If all values are treated as unsigned, the order would be [0, 1, 2, -2, -1] instead.
+ */
+@Retention(RetentionPolicy.CLASS)
+@Target(ElementType.FIELD)
+public @interface Unsigned {
+}