title: Why are interface method invocations slower than concrete invocations?
body: <p>This is question comes in mind when I finding difference between abstract class and interface.
  In <a href="http://gcc.gnu.org/ml/java/1999-q4/msg00305.html" rel="noreferrer">this post</a> I came to know that interfaces are slow as they required extra indirection.
  But I am not getting what type of indirection required by the interface and not by the abstract class or concrete class.Please clarify on it.
  Thanks in advance</p>