title: What is the use of "System.out::println" in Java 8
body: <p>I saw a code in java 8 to iterate a collection.</p>
  
  <pre><code>List&lt;Integer&gt; numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
  numbers.forEach(System.out::println);
  </code></pre>
  
  <p>What is the functionality of <code>System.out::println</code> ? And how the above code can iterate through the List. </p>
  
  <p>And what is the use of the operator <code>::</code> , Where else we can use this operator ?</p>