title: Clarification regarding setContentView
body: <p>What is difference between:</p>
  
  <pre><code>setContentView(R.layout.activity_main);        
  TextView txtView = (TextView)findViewById(R.id.text); 
  </code></pre>
  
  <p>And</p>
  
  <pre><code>TextView textView = new TextView(this);
  setContentView(textView);
  </code></pre>
  
  <p>I found these two pieces of code. In first the <code>setContentView</code> has a I'd passed to it about layout. And in second case it has a view passed as argument. Is textView also an id. I think the difference is that in first case, it is layout of activity_main as described in XML file(which contains textView as well) and in second case it is id of textView. Tell me if I am correct. </p>
  
  <p>Also tell me what does 'this' refer to here. Why we are using  <code>findViewById</code> in first case?</p>