title: Apache Beam: Trigger for Fixed Window
body: <p>According to <a href="https://beam.apache.org/releases/javadoc/2.6.0/org/apache/beam/sdk/transforms/windowing/Window.html" rel="nofollow noreferrer">following</a> documentation, it is stated that if you don't explicitly specify a trigger you get behavior described below:</p>
  <blockquote>
  <p>If unspecified, the default behavior is to trigger first when the
  watermark passes the end of the window, and then trigger again every
  time there is late arriving data.</p>
  </blockquote>
  <p>Is this behavior true for FixedWindow as well? For example you would assume fixed window should have a default trigger of repeatedly firing after watermark passes end of window, and discard all late data unless late data is explicitly handled. Also where in the source code can I see definition of trigger for, example FixedWindow object?</p>