title: Java 8 FunctionalInterface and Interface
body: <p><a href="https://i.stack.imgur.com/LjDdy.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/LjDdy.png" alt="enter image description here" /></a></p>
  <p>Hello guys. What is difference between <code>FunctionInterface</code> and <code>Interface</code> why we need declare
  <code>@FunctionalInterface</code> if we have interface in this implementation of package <code>java.util.function</code>;</p>