AlertDialog.Builder builder = new AlertDialog.Builder(this);              builder.setTitle("你确定要退出吗?");              builder.setPositiveButton("确定",new DialogInterface.OnClickListener() {                                @Override                public void onClick(DialogInterface dialog, int which) {                    // TODO Auto-generated method stub                    System.exit(0);                 }            });                           builder.setNegativeButton("取消", new DialogInterface.OnClickListener() {                                @Override                public void onClick(DialogInterface dialog, int which) {                    // TODO Auto-generated method stub                      return;                }            });                             builder.show();