构建方法返回String的报错问题

//返回文件大小的字符串
public String getSize(String fileName){
String size="";
try{
long l = 0;
String path = fileName;
File ff = new File(path);
if (ff.isDirectory()) { //如果路径是文件夹的时候
l = getFileSize(ff);
size=FormetFileSize(l);
} else {
l = getFileSizes(ff);
size=FormetFileSize(l);
}
} catch (Exception e){
e.printStackTrace();
}
return size;
}