응용 프로그램을 종료하는 2가지 방법

@Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        //     
        if(keyCode == KeyEvent.KEYCODE_BACK){
            AlertDialog.Builder dialog = new AlertDialog.Builder(this);
            dialog.setTitle("  ");
            dialog.setMessage("          ？");
            dialog.setPositiveButton("  ",new DialogInterface.OnClickListener(){
                @Override
                public void onClick(DialogInterface dialog, int which) {
                   finish();
                }
            });
            dialog.setNegativeButton("  ",new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                      return ;
                }
            });
            dialog.show();
        }
        
        return super.onKeyDown(keyCode, event);
    }

private long existTime = 0;
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        //     
        if(keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_DOWN){
           if(System.currentTimeMillis()-existTime > 2000){
               Toast.makeText(this,"        ",Toast.LENGTH_SHORT).show();
               existTime =  System.currentTimeMillis();
           }else {
               finish();
           }
           return true; //  
        }
        return super.onKeyDown(keyCode, event);
    }