doublebackAndroid

doubleback.java

private static final int TIME_DELAY = 2000;
private static long back_pressed;
@Override
public void onBackPressed() {
    if (back_pressed + TIME_DELAY > System.currentTimeMillis()) {
        super.onBackPressed();
    } else {
        Toast.makeText(getBaseContext(), "Press once again to exit!",
                Toast.LENGTH_SHORT).show();
    }
    back_pressed = System.currentTimeMillis();
}