Remove last line from a StringBuilder without knowing the number of characters

Question

I want to know if there exists a simple method for removing the last line from a StringBuilder object without knowing the number of characters in the last line.

Example:

Hello, how are you?
Fine thanks!
Ok, Perfect...

I want to remove "Ok, Perfect..."

Answer 1

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

EDIT: If you want to remove the last non-empty line do

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

Answer 2

Depending on how your Strings are constructed and what your goal is, it may be easier to not add the last line to the StringBuilder instead of removing it.