title: Is Comparable Interface a FunctionalInterface?
body: <p>I am using decompiler tools when I look at Comparable it has one abstract method and not have <code>FunctionalInterface</code> annotation </p>
  
  <pre><code>public interface Comparable&lt;T&gt; {
      int compareTo(T var1);
  }
  </code></pre>
  
  <p>same like Comparator, but comparator have <code>FunctionalInterface</code> annotation </p>
  
  <pre><code>    @FunctionalInterface
      public interface Comparator&lt;T&gt; {
      int compare(T var1, T var2);
      ... 
  }
  </code></pre>