title: Optional Methods in Java Interface
body: <p>From my understanding if you implement an interface in java, the methods specified in that interface have to be used by the sub classes implementing the said interface.</p>
  
  <p>I've noticed that in some interfaces such as the Collection interface there are methods which are commented as optional, but what exactly does this mean? Its thrown me a bit as I thought all methods specified in the interface would be required?</p>