1 files changed, 96 insertions, 0 deletions
diff --git a/java/src/main/java/com/google/protobuf/Extension.java b/java/src/main/java/com/google/protobuf/Extension.java
new file mode 100644
index 0000000..0baa22b
--- /dev/null
+++ b/java/src/main/java/com/google/protobuf/Extension.java
@@ -0,0 +1,96 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+/**
+ * Interface that generated extensions implement.
+ *
+ * @author liujisi@google.com (Jisi Liu)
+ */
+public abstract class Extension<ContainingType extends MessageLite, Type> {
+  /** Returns the field number of the extension. */
+  public abstract int getNumber();
+
+  /** Returns the type of the field. */
+  public abstract WireFormat.FieldType getLiteType();
+
+  /** Returns whether it is a repeated field. */
+  public abstract boolean isRepeated();
+
+  /** Returns the descriptor of the extension. */
+  public abstract Descriptors.FieldDescriptor getDescriptor();
+
+  /** Returns the default value of the extension field. */
+  public abstract Type getDefaultValue();
+
+  /**
+   * Returns the default instance of the extension field, if it's a message
+   * extension.
+   */
+  public abstract MessageLite getMessageDefaultInstance();
+
+  // All the methods below are extension implementation details.
+
+  /**
+   * The API type that the extension is used for.
+   */
+  protected enum ExtensionType {
+    IMMUTABLE,
+    MUTABLE,
+    PROTO1,
+  }
+
+  protected ExtensionType getExtensionType() {
+    // TODO(liujisi): make this abstract after we fix proto1.
+    return ExtensionType.IMMUTABLE;
+  }
+
+  /**
+   * Type of a message extension.
+   */
+  public enum MessageType {
+    PROTO1,
+    PROTO2,
+  }
+  
+  /**
+   * If the extension is a message extension (i.e., getLiteType() == MESSAGE),
+   * returns the type of the message, otherwise undefined.
+   */
+  public MessageType getMessageType() {
+    return MessageType.PROTO2;
+  }
+
+  protected abstract Object fromReflectionType(Object value);
+  protected abstract Object singularFromReflectionType(Object value);
+  protected abstract Object toReflectionType(Object value);
+  protected abstract Object singularToReflectionType(Object value);
+}