On clicking quit button on alert dialog shows MainActivity

Question

onBackPressed shows the alertDialog. On clicking the quit button it shows the Main Activity. Again when back key is pressed alertDialog is shown but this time on clicking quit button closes the application. What am I missing?

Here is the OpenExitDialog() Code.

public void OpenExitDialog()    {

    try {
        com.heyzap.sdk.ads.InterstitialAd.fetch();
        if (com.heyzap.sdk.ads.InterstitialAd.isAvailable()) {
            com.heyzap.sdk.ads.InterstitialAd.display(MainActivity.this);
        } else {
            start_AppAd.loadAd(new AdEventListener() {
                @Override
                public void onReceiveAd(Ad ad) {
                    start_AppAd.showAd(new AdDisplayListener() {
                        @Override
                        public void adHidden(Ad ad) { }
                        @Override
                        public void adDisplayed(Ad ad) { }

                        @Override
                        public void adClicked(Ad arg0) { }
                        @Override
                        public void adNotDisplayed(Ad arg0) { }
                    });
                }
                @Override
                public void onFailedToReceiveAd(Ad ad) {

                }
            });
        }
        try {
            AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
            builder.setTitle("Exit");
            builder.setIcon(R.mipmap.ic_launcher);
            builder.setMessage("Thankyou!")
                    .setCancelable(false)
  }
                    })

                    .setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialogInterface, int i) {
                            dialogInterface.cancel();
                        }
                    })
                    .setPositiveButton("Quit", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialogInterface, int i) {
                            finish();
                        }
                    });
            AlertDialog alert = builder.create();
            alert.show();

        } catch (Exception e) {
            e.printStackTrace();
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

Answer 1

Try this,

    @Override
    public void onBackPressed() {

               AlertDialog alertbox = new AlertDialog.Builder(this)
    .setMessage("Do you want to exit application?")
    .setPositiveButton("Quit", new DialogInterface.OnClickListener() {

        // do something when the button is clicked
        public void onClick(DialogInterface arg0, int arg1) {

            finish();
            //close();


        }
    })
    .setNegativeButton("Cancel", new DialogInterface.OnClickListener() {

        // do something when the button is clicked
        public void onClick(DialogInterface arg0, int arg1) {
                       }
    })
      .show();

 }

Hope it's useful.

Answer 2

.setPositiveButton("Quit", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialogInterface, int i) {
                            finish();
                            System.exit(0);  //add this line

                        }
                    });