Trimming multiple characters in a string

Question

My program reads some strings from file which have to be post processed. The original text in the file looks like

A1DY^
BLKSS^
"GH67^"^

Where ^ is the space character I used to demonstrate. As you can see all words in the file end with space. Some words are in double quote. I want to store these strings in my program

A1DY
BLKSS
GH67

In other words, I want to trim all spaces and double quotes. If I use str.trim(); it will remove the last space. So, the third line will be "GH67^". I also used str.replaceAll("^\"|\"$", ""); to trim the double quotes. The result is GH67^. That means, I have to trim it again.

Is there any better way to remove all spaces and double quotes at once? Note that I don't want to extract alphanumeric characters. I want to trim special characters.

Will this work? https://stackoverflow.com/questions/1805518/replacing-all-non-alphanumeric-characters-with-empty-strings — Gaurav Bhor, May 16 '17 at 20:21
That extracts alphanumeric. If I have `DS-DK^` in the file I want to save `DS-DK`. — mahmood, May 16 '17 at 20:23
Using '\0' instead of spaces might be more useful, since '\0' is never used as a character. — AppWriter, May 16 '17 at 20:25

shmosel · Accepted Answer · 2017-05-16T20:32:44.313

4

This will trim any number of quotes or spaces from the beginning or end of your string:

str = str.replaceAll("^[ \"]+|[ \"]+$", "");

edited May 16 '17 at 20:32

answered May 16 '17 at 20:27

shmosel

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To prevent common newbie mistake, add `str =` in front. – Andreas May 16 '17 at 20:30
Technically, removing leading spaces is counter to OPs requirements, but it likely makes no difference. – Andreas May 16 '17 at 20:35
@Andreas Where are you seeing that? – shmosel May 16 '17 at 20:36
OP said *"As you can see all words in the file **end with** space"*. Sure, OP also tried to use `trim()`, which trims from both ends, but doesn't mean that using `trim()` would have been right, but since OP didn't think `trim()` would be wrong, there will probably never be leading spaces that needs to be retained, which is why I said *"it likely makes no difference"*, and I left my up-vote in place. – Andreas May 16 '17 at 20:42

score 0 · Answer 2 · answered May 16 '17 at 20:55

In a strict interpretation of your question description, you only want trailing spaces removed, not leading spaces and not other whitespace characters like tabs (\t).

Also, a strict trimming function will only remove double-quotes if both a leading and a trailing pair is found, and only one such set.

If double-quotes are present, trailing spaces inside the double-quotes should also be removed.

To accomplish all that, strictly, in a single regex operation, do this:

str = str.replaceFirst("^(\"?)(.*?) *\\1 *$", "$2");

This regex uses the ^ and $ anchors to ensure it only matches against the entire string.

The leading " is optional, and matched as capture group 1, if present. The trailing " is only matched if leading " was matched, and leading " is only matched if trailing " is matched. This is done using a \1 backreference to the optional leading ". If matched, they will be removed from the result.

No leading spaces are removed, but any trailing spaces before and/or after the optional trailing " are removed.

Anything not removed is captured in group 2, and retained in the replacement string.

Trimming multiple characters in a string

2 Answers2