Example back button android studio

Anda tinggal menambahkan barisan source berikut untuk membuat back button :

boolean doubleBackToExitPressedOnce = false;
@Override
public void onBackPressed() {
    if (doubleBackToExitPressedOnce) {
        super.onBackPressed();
        return;
    }
    this.doubleBackToExitPressedOnce = true;
    Toast.makeText(this, "Please click BACK again to exit", Toast.LENGTH_SHORT).show();
    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {
            doubleBackToExitPressedOnce=false;                    
        }
    }, 2000);
}