Java : com.google.protobuf does not exist

I try to install Walkaround, a project based on Google Wave. I followed the official wiki for installation.

But during the last step (./runant run), I've 100 errors:

Proto.java:7: package com.google.protobuf does not exist
      com.google.protobuf.ExtensionRegistry registry) {
                         ^
Proto.java:12450: package com.google.protobuf.Descriptors does not exist
  private static com.google.protobuf.Descriptors.Descriptor
                                                ^
Proto.java:12453: package com.google.protobuf.GeneratedMessage does not exist
    com.google.protobuf.GeneratedMessage.FieldAccessorTable

...
...
100 errors

Similar topic: Problems using protobufs with java and scala. So I try this solution after searching a proto.jar and the Proto.java:

javac -cp 
    ~/walkaround/third_party_src/wave/trunk/dist/proto.jar
    ~/walkaround/proto_src/com/google/walkaround/proto/Proto.java

But I get the same 100 errors.

Someone can help me? I have no knowledge about Ubuntu Linux and Java environment.

I had the same problem. The reason on my Project was that ./get-third-party-deps failed. That was fixed by installing build-essential on my ubuntu machine

sudo apt-get install build-essential
./get-third-party-deps