java – 在不知道字符数的情况下从StringBuilder中删除最后一行

StringBuilder sb = new StringBuilder("Hello,how are you?nFine thanks!nOk,Perfect...");

int last = sb.lastIndexOf("n");
if (last >= 0) { sb.delete(last,sb.length()); }

http://ideone.com/9k8Tcj

编辑：如果你想删除最后一个非空行吗

StringBuilder sb = new StringBuilder(
        "Hello,Perfect...nn");
if (sb.length() > 0) {
    int last,prev = sb.length() - 1;
    while ((last = sb.lastIndexOf("n",prev)) == prev) { prev = last - 1; }
    if (last >= 0) { sb.delete(last,sb.length()); }
}

http://ideone.com/AlzQe0