title: What means 1L serialVersionUID? When could I use this default value 1L?
body: <p>There are 3 ways to define the serialVersionUID :</p>
  
  <pre><code>1. private static final long serialVersionUID = 1L; (Default)
  2. private static final long serialVersionUID = -8940196742313994740L; (Generated)
  3. Don't define serialVersionUID and let the JVM define it at runtime. @Lance Java
  </code></pre>
  
  <p>But I don't understand the first way!</p>
  
  <p>I have seen it already, that somebody defines "serialVersionUID=1L" for all java-classes in source code.</p>
  
  <p>What is the meaning? Is that useful?</p>
  
  <p>If all classes have the same serialVersionUID 1L, is there no problem?</p>