Construction. 

AnExampleMessage.Builder messageBuilder;
messageBuilder = AnExampleMessage.newBuilder ();
messageBuilder = AnExampleMessage.newBuilder (another_message);
AnExampleMessage message = messageBulder.build ();

Singular Fields. 

System.out.println (message.getSomeInteger ());
messageBuilder.setSomeInteger (1234);
if (message.hasOptionalInteger ()) {
    messageBuilder = message.toBuilder ();
    messageBuilder.clearOptionalInteger ();
}

Repeated Fields. 

int size = messages.getMessagesCount ();
AnExampleMessage message = messages.getMessages (1234);
List<AnExampleMessage> messageList = messages.getMessagesList ();
messagesBuilder.addMessages (messageBuilder);
messagesBuilder.addMessages (message);

Byte Array Serialization. 

byte [] buffer = message.toByteArray ();
try {
    AnExampleMessage message = AnExampleMessage.parseFrom (buffer);
} catch (InvalidProtocolBufferException e) {
    System.out.println (e);
}

Standard Stream Serialization. 

message.writeTo (stream);
AnExampleMessage message = AnExampleMessage.parseFrom (stream);