title: java PECS List<? super T> dest and List<T> dest difference?
body: <pre><code>public static &lt;T&gt; void copy1(List&lt;? extends T&gt; src, List&lt;? super T&gt; dest) {
      for (int i = 0; i &lt; src.size(); i++) {
          dest.add(src.get(i));
      }
  }
  
  public static &lt;T&gt; void copy2(List&lt;? extends T&gt; src, List&lt;T&gt; dest) {
      for (int i = 0; i &lt; src.size(); i++) {
          dest.add(src.get(i));
      }
  }
  </code></pre>
  
  <p>top 2 method both can implements PECS Effect，but what difference ??</p>
  
  <p>thank you !!</p>