Back button pressed

I have multiple activities with 5 different screens.How should i handle a situation if a back key is pressed ??in First Screen and other screens ?? finish() and System.exit() is not working ..What should i do to exit my application if the Back button is pressed ?? The below coding does not work ?Please suggest me a way to exit an application having multiple screens ``` public boolean onKeyDown(int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_BACK) { AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder( this); new AlertDialog.Builder(this) .setMessage("Are you sure you want to exit?") .setCancelable(true) .setPositiveButton("Yes", new DialogInterface.OnClickListener() { public void onClick(DialogInterface hi, int dd) { Intent exitIntent = new Intent(Mapper.this,SplashActivity.class); exitIntent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP|Intent.FLAG_ACTIVITY_CLEAR_TOP); SplashActivity.mHandler.sendEmptyMessage(0); startActivity(exitIntent); } } ) .setNegativeButton("Cancel", new DialogInterface.OnClickListener() { public void onClick(DialogInterface hi, int dd) { } } ); AlertDialog alertDialog = alertDialogBuilder.create(); // show it alertDialog.show(); //AlertDialog alert1 = alt_bld.create(); //alert1.setTitle("EXIT"); //alert1.show(); return true; } return super.onKeyDown(keyCode, event); } And in Start.Class: public boolean onKeyDown(int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_BACK || keyCode == KeyEvent.KEYCODE_HOME) { mHandler.removeCallbacksAndMessages(null); SplashActivity.this.finish(); } return super.onKeyDown(keyCode, event); } ```