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+<html devsite>
+  <head>
+    <title>Exporting Constants</title>
+    <meta name="project_path" value="/_project.yaml" />
+    <meta name="book_path" value="/_book.yaml" />
+  </head>
+  <body>
+  <!--
+      Copyright 2017 The Android Open Source Project
+
+      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.
+  -->
+
+<p>In cases where an interface is not Java-compatible (because it uses unions
+for example) it may still be desirable to export the constants (enum values) to
+the Java world. This scenario is supported by <code>hidl-gen -Ljava-constants
+&hellip;</code> which extracts annotated enum declarations from the interface
+file(s) in a package and produces a java library named
+<code>[PACKAGE-NAME]-V[PACKAGE-VERSION]-java-constants</code>. Annotate each
+enum declaration to be exported as follows:</p>
+
+<pre class="prettyprint">
+@export
+enum Foo : int32_t {
+  SOME_VALUE,
+  SOME_OTHER_VALUE,
+};
+</pre>
+
+<p>If necessary, the name under which this type is exported to the Java world
+can be different from that chosen in the interface declaration by adding the
+annotation-parameter <code>name</code>:</p>
+
+<pre class="prettyprint">
+@export(name="JavaFoo")
+enum Foo : int32_t {
+  SOME_VALUE,
+  SOME_OTHER_VALUE,
+};
+</pre>
+
+<p>If Java conventions or personal preference ask for a common prefix to be
+added to the enum type's values, use the annotation-parameter
+<code>value_prefix</code>:</p>
+
+<pre class="prettyprint">
+// File "types.hal".
+
+package android.hardware.bar@1.0;
+
+@export(name="JavaFoo", value_prefix="JAVA_")
+enum Foo : int32_t {
+  SOME_VALUE,
+  SOME_OTHER_VALUE,
+};
+</pre>
+
+<p>The resulting Java class appears as follows:</p>
+
+<pre class="prettyprint">
+package android.hardware.bar.V1_0;
+
+public class Constants {
+  public final class JavaFoo {
+    public static final int JAVA_SOME_VALUE = 0;
+    public static final int JAVA_SOME_OTHER_VALUE = 1;
+  };
+};
+</pre>
+
+<p>Finally, Java type declaration for enum types declared in
+<code>types.hal</code> are grouped inside a class <code>Constants</code> in the
+given package. Enum types declared as children of an interface will be grouped
+under that interface's Java class declaration.</p>
+
+  </body>
+</html>