2.1/user/src/com/google/gwt/user/tools/RpcAsyncClientTemplate.javasrc

package @clientPackage;

import com.google.gwt.user.client.rpc.AsyncCallback;

/**
 * The async counterpart of <code>GreetingService</code>.
 */
public interface GreetingServiceAsync {
  void greetServer(String input, AsyncCallback<String> callback)
      throws IllegalArgumentException;
}