title: What is a serialVersionUID and why should I use it?
body: <p>Eclipse issues warnings when a <code>serialVersionUID</code> is missing.  </p>
  
  <blockquote>
    <p>The serializable class Foo does not declare a static final
    serialVersionUID field of type long</p>
  </blockquote>
  
  <p>What is <code>serialVersionUID</code> and why is it important?  Please show an example where missing <code>serialVersionUID</code> will cause a problem.</p>