title: setContentView throws NullPointerException
body: <p>I have an MainActivity and an extended DsiplayClass. Out of this DisplayClass I wanted to change the ContentView via setContentView, but all I got is an NullPointerException.</p>
  
  <p>Please help me and tell me why.</p>
  
  <p><strong>MainActivity:</strong></p>
  
  <pre><code>public class Main extends Activity {
  
      DisplayClass display;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
  
          display = new DisplayClass();
  
          display.showMain();
      }
  
  }
  </code></pre>
  
  <p><strong>DisplayClass:</strong></p>
  
  <pre><code>public class DisplayClass extends Main {
  
      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
      }
  
      public void DisplayClass() {
  
      }
  
      public void showMain() {
          setContentView(R.layout.mainmenu);
      }
  
  }
  </code></pre>
  
  <p>NullPointerException is caused in the line where I set the "setContentView(R.layout.mainmenu);" and in this line "display.showMain();".</p>
  
  <p>Please help me.</p>