执行以下程序后的输出结果是（）

public class Test {

    public static void main(String[] args) {

        StringBuffer a = new StringBuffer("A");

        StringBuffer b = new StringBuffer("B");

        operator(a, b);

        System.out.println(a + "," + b);

    }

    public static void operator(StringBuffer x, StringBuffer y) {

        x.append(y); y = x;

    }

}