title: struggling with class, extends and implements
body: <p>I'm really struggling with classes, extend and implement.</p>
  
  <p>Well at android I want to create a preference screen and check the user input.</p>
  
  <p>I can use therefore a file named preferences.class and do everything I need with the following class:</p>
  
  <pre><code>        public class Preferences extends PreferenceActivity implements OnSharedPreferenceChangeListener {
  
          @Override
  protected void onCreate(Bundle savedInstanceState) {
  }
  
        @Override
        public void onSharedPreferenceChanged(SharedPreferences sp, String key) {
      }
  }
  </code></pre>
  
  <p>But isn't it better to split this up in different classes? and if yes how?</p>