StringBuffer问题

Java code

public static void main(String[] args)    {        String a = "{\"deviceList\":[{\"deviceAliasName\":\"QQ\",\"deviceID\":\"lifanghua11\",\"deviceType\":\"1\",\"terminalType\":\"terminaltype\"}],\"returnCode\":\"0\",\"returnDesc\":\"Success\"}";        StringBuffer buffer = new StringBuffer(a);        buffer.insert(a.indexOf("["), "@");        buffer.insert(a.lastIndexOf("]")            + NumContants.TWO.getValue(), "@");        System.out.println(a.toString());    }

为什么输出地结果是:{"deviceList":[{"deviceAliasName":"QQ","deviceID":"lifanghua11","deviceType":"1","terminalType":"terminaltype"}],"returnCode":"0","returnDesc":"Success"}
@没有加上去.新人,求指点

[解决办法]
System.out.println(buffer);
[解决办法]
StringBuffer对象已经改变了，但是String a是没有改变的，呵呵。
楼主小心了。
[解决办法]
楼主粗心了，你最后输出的是a啊，不是buffer，要检查检查……
[解决办法]
System.out.println(buffer.toString());
[解决办法]
String a = "{\"deviceList\":[{\"deviceAliasName\":\"QQ\",\"deviceID\":\"lifanghua11\",\"deviceType\":\"1\",\"terminalType\":\"terminaltype\"}],\"returnCode\":\"0\",\"returnDesc\":\"Success\"}";
StringBuffer buffer = new StringBuffer(a);

buffer.insert(a.indexOf("["), "@");
buffer.insert(a.lastIndexOf("]")
+ NumContants.TWO.getValue(), "@");
System.out.println(a.toString());
代码没有问题，输出的不是自己的结果。。。