public static void main(String[] args) {
StringBuilder b1 = new StringBuilder("a");
StringBuilder b2 = new StringBuilder("b");
op(b1,b2);
System.out.println(b1+","+b2); // 结果为 ab,b 为什么??
}
public static void op(StringBuilder b1, StringBuilder b2){
b1.append(b2);
b2 = b1;
}