code: public synchronized static GlobusCredential getDefaultCredential() throws GlobusCredentialException {
          if (defaultCred == null) {
              reloadDefaultCredential();
          } else if (!credentialSet) {
              if (credentialFile.lastModified() == credentialLastModified) {
                  defaultCred.verify();
              } else {
                  defaultCred = null;
                  reloadDefaultCredential();
              }
          }
          return defaultCred;
      }
docs: Returns the default credential. The default credential is usually the user proxy certificate. <BR>
  The credential will be loaded on the initial call. It must not be expired. All subsequent calls to this
  function return cached credential object. Once the credential is cached, and the underlying file
  changes, the credential will be reloaded.
  
  @return the default credential.
  @exception GlobusCredentialException
  if the credential expired or some other error with the credential.