title: IllegalArgumentException: file contains path separator
body: <p>I'm trying to check whether a zip exists in a subdirectory in the application's internal storage:</p>
  
  <pre><code>File file = this.getApplicationContext().getFileStreamPath(this.getFilesDir().getAbsolutePath() + "/thesubdirectory/the.zip";
  if(file.exists()) {
      Log.e(this.class.getName(), "file exists");
  }
  </code></pre>
  
  <p>This is throwing a <code>java.lang.IllegalArgumentException: File /data/data/my.package.name/files/thesubdirectory/the.zip contains a path separator</code>.</p>
  
  <p>Why is this happening? I thought this was the way you <em>should</em> check whether a file exists.</p>