title: Why Functional Interfaces in Java 8 have one Abstract Method?
body: <p>As we know in Java 8, the concept of functional interfaces are introduced. A Functional Interface has one <code>abstract</code> method and several default or static methods are possible. </p>
  
  <p>But why should a Functional interface have only one abstract method? 
  If Interface has more then one abstract method, why is this not a Functional Interface? </p>