Android双击两次返回按钮退出程序

private boolean doubleBackToExitPressedOnce = false; 
 
@Override 
protected void onResume() { 
    super.onResume(); 
    // .... other stuff in my onResume .... 
    this.doubleBackToExitPressedOnce = false; 
} 
 
@Override 
public void onBackPressed() { 
    if (doubleBackToExitPressedOnce) { 
        super.onBackPressed(); 
        return; 
    } 
    this.doubleBackToExitPressedOnce = true; 
    Toast.makeText(this, R.string.exit_press_back_twice_message, Toast.LENGTH_SHORT).show(); 
}