code: private void uploadSampleFile() {
          mDialog = ProgressDialog.show(MainActivity.this, getText(R.string.boxsdk_Please_wait), getText(R.string.boxsdk_Please_wait));
          new Thread() {
              @Override
              public void run() {
                  try {
                      String uploadFileName = "box_logo.png";
                      InputStream uploadStream = getResources().getAssets().open(uploadFileName);
                      String destinationFolderId = "0";
                      String uploadName = "BoxSDKUpload.png";
                      BoxRequestsFile.UploadFile request = mFileApi.getUploadRequest(uploadStream, uploadName, destinationFolderId);
                      final BoxFile uploadFileInfo = request.send();
                      showToast("Uploaded " + uploadFileInfo.getName());
                      loadRootFolder();
                  } catch (IOException e) {
                      e.printStackTrace();
                  } catch (BoxException e) {
                      e.printStackTrace();
                      BoxError error = e.getAsBoxError();
                      if (error != null && error.getStatus() == HttpURLConnection.HTTP_CONFLICT) {
                          ArrayList<BoxEntity> conflicts = error.getContextInfo().getConflicts();
                          if (conflicts != null && conflicts.size() == 1 && conflicts.get(0) instanceof BoxFile) {
                              uploadNewVersion((BoxFile) conflicts.get(0));
                              return;
                          }
                      }
                      showToast("Upload failed");
                  } finally {
                      mDialog.dismiss();
                  }
              }
          }.start();
  
      }
docs: Method demonstrates a sample file being uploaded using the file api