title: How to define an immutable object in a mutable Java class?
body: <p>In a class, I want to define an empty object and use it anywhere we need it. This object needs to be immutable to avoid accidentally modification. If this object is defined as a <code>public static final</code> member of the class, the object could be changed if the class itself is mutable.</p>
  
  <p>What's the good way to create an immutable object in a mutable class?</p>