android 开发中文件名错误

Integer val = myReceipt.receiptId ;
            String fileName = "image" + "_" + title.getText().toString()+"_" + val.toString(); 
            photo = this.createTemporaryFile(fileName, ".jpg");
            intent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(photo));
            uriOfPhoto = Uri.fromFile(photo);
            startActivityForResult(intent, RESULT_CAMERA_SELECT);
          }
        }
    private File createTemporaryFile(String part, String ext) throws Exception
    {
        File tempDir = new File (Environment.getExternalStorageDirectory() + "/Catch All Keeper/Receipts");
        if(!tempDir.exists())
        {
            tempDir.mkdir();
        }
        tempDir.canWrite();
        return File.createTempFile(part, ext, tempDir);
    }
});

我用上面的代码应该给出文件名image_title_val，但是却给出一个奇怪的名字image_title_(some random numbers).jpg。
为什么出现这个问题?