How to quit android application programmatically

I Found some codes for quit an Android application programatically. By calling any one of the following code in onDestroy() will it quit application entirely?

1. System.runFinalizersOnExit(true)
   (OR)
2. android.os.Process.killProcess(android.os.Process.myPid());

I dont want to run my application in background after clicking quit button. Pls suggest me can i use any one of these code to quit my app? If so which code can i use? Is it good way to quit the app in Android?

Since API 16 you can use the finishAffinity method, which seems to be pretty close to closing all related activities by its name and Javadoc description:

this.finishAffinity();

Finish this activity as well as all activities immediately below it in the current task that have the same affinity. This is typically used when an application can be launched on to another task (such as from an ACTION_VIEW of a content type it understands) and the user has used the up navigation to switch out of the current task and into its own task. In this case, if the user has navigated down into any other activities of the second application, all of those should be removed from the original task as part of the task switch.

Note that this finish does not allow you to deliver results to the previous activity, and an exception will be thrown if you are trying to do so.

Since API 21 you can use a very similar command

finishAndRemoveTask();

Finishes all activities in this task and removes it from the recent tasks list.

getActivity().finish();
System.exit(0);

this is the best way to exit your app.!!!

The best solution for me.

finishAffinity();

System.exit(0);

If you will use only finishAffinity(); without System.exit(0); your application will quit but the allocated memory will still be in use by your phone, so... if you want a clean and really quit of an app, use both of them.

This is the simplest method and works anywhere, quit the app for real, you can have a lot of activity opened will still quitting all with no problem.

example on a button click

public void exitAppCLICK (View view) {

    finishAffinity();
    System.exit(0);

}

or if you want something nice, example with an alert dialog with 3 buttons YES NO and CANCEL

// alertdialog for exit the app
AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);

// set the title of the Alert Dialog
alertDialogBuilder.setTitle("your title");

// set dialog message
alertDialogBuilder
        .setMessage("your message")
        .setCancelable(false)
        .setPositiveButton("YES"),
                new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog,
                                        int id) {
                        // what to do if YES is tapped
                        finishAffinity();
                        System.exit(0);
                    }
                })

        .setNeutralButton("CANCEL"),
                new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog,
                                        int id) {
                        // code to do on CANCEL tapped
                        dialog.cancel();
                    }
                })

        .setNegativeButton("NO"),
                new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog,
                                        int id) {
                        // code to do on NO tapped
                        dialog.cancel();
                    }
                });

AlertDialog alertDialog = alertDialogBuilder.create();

alertDialog.show();

Please think really hard about if you do need to kill the application: why not let the OS figure out where and when to free the resources?

Otherwise, if you're absolutely really sure, use

finish();

As a reaction to @dave appleton's comment: First thing read the big question/answer combo @gabriel posted: Is quitting an application frowned upon?

Now assuming we have that, the question here still has an answer, being that the code you need if you are doing anything with quitting is finish(). Obviously you can have more than one activity etc etc, but that's not the point. Lets run by some of the use-cases

1. You want to let the user quit everything because of memory usage and "not running in the background? Doubtfull. Let the user stop certain activities in the background, but let the OS kill any unneeded recourses.
2. You want a user to not go to the previous activity of your app? Well, either configure it so it doesn't, or you need an extra option. If most of the time the back=previous-activity works, wouldn't the user just press home if he/she wants to do something else?
3. If you need some sort of reset, you can find out if/how/etc your application was quit, and if your activity gets focus again you can take action on that, showing a fresh screen instead of restarting where you were.

So in the end, ofcourse, finish() doesn't kill everthing, but it is still the tool you need I think. If there is a usecase for "kill all activities", I haven't found it yet.

Create a ExitActivity and declare it in manifest. And call ExitActivity.exit(context) for exiting app.

public class ExitActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        finish();
    }

    public static void exit(Context context) {
        Intent intent = new Intent(context, ExitActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
        context.startActivity(intent);
    }

}