title: Sort only even numbers in array and do not touch odds
body: <p>So I have an array of integers and the exercise tells me to sort only even elements. I understand this can be easily achieved by plain checking each element, which is probably O(n^2).<br>
  What I am trying to do is to write a comparator which takes only even numbers as parameters and then sort the whole array with it.  </p>
  
  <pre><code>Comparator&lt;Integer&gt; comp = new Comparator&lt;&gt;() {
          @Override
          public int compare(Integer o1, Integer o2) {
              return o1.compareTo(o2);
          }
      };
  Arrays.sort(array, comp));
  </code></pre>
  
  <p>Is there any way to do so?
  Thank you </p>