title: Don't know why "Dialog Box" is not appearing? Even "Toast" Statement is not running
body: <p>I Have just started learning Android, this is the code of my java file. I have not changed the XML file. On running this code, simple blank activity is shown, with no DialogBox. Help needed.   </p>
  
  <pre><code>package com.example.dialogbox;
  
  import android.app.Activity;
  import android.app.AlertDialog;
  import android.content.DialogInterface;
  import android.os.Bundle;
  
  public class MainActivity extends Activity {
  
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      Add("Exit App", "Are u sure?");
      Toast.makeText(this, "open", Toast.LENGTH_LONG);
  }
  
  public void Add(String title, String msg) {
      Toast.makeText(this, "open", Toast.LENGTH_LONG);
      AlertDialog.Builder builder = new AlertDialog.Builder(this);
      builder.setTitle(title)
              .setMessage(msg)
              .setPositiveButton("Yes",
                      new DialogInterface.OnClickListener() {
  
                          public void onClick(DialogInterface dialog,
                                  int which) {
                              // TODO Auto-generated method stub
  
                          }
                      })
              .setNegativeButton("No", new DialogInterface.OnClickListener() {
  
                  public void onClick(DialogInterface dialog, int which) {
                      // TODO Auto-generated method stub
  
                  }
              });
      AlertDialog alert = builder.create();
  
  }
  
  }  
  </code></pre>