title: Why ArrayList.this.modCount is different from this.modCount
body: <p>In the source codes of ArrayList,I found some puzzled codes following:</p>
  
  <pre><code>public int size() {
          if (ArrayList.this.modCount != this.modCount)
              throw new ConcurrentModificationException();
          return this.size;
  }
  </code></pre>
  
  <p>The modCount is inherited from  <strong>AbstractList</strong>.I can't find another modCount.So I think the <strong>ArrayList.this.modCount</strong> is the same as the <strong>this.modCount</strong>.But actually,<strong>ArrayList.this.modCount != this.modCount</strong> can be true!</p>
  
  <p>Why don't the same variable  equal to itself?</p>
  
  <p>=====================================================================</p>
  
  <p>The code is in the <code>SubList</code> class.It's my mistake.</p>