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.

That extracts alphanumeric. If I have DS-DK^ in the file I want to save DS-DK. — mahmood
– mahmood, Commented May 16, 2017 at 20:23
Using '\0' instead of spaces might be more useful, since '\0' is never used as a character. — AppWriter
– AppWriter, Commented May 16, 2017 at 20:25

shmosel · Accepted Answer · 2017-05-16 20:32:44Z

4

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

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

edited May 16, 2017 at 20:32

answered May 16, 2017 at 20:27

shmosel

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4 Comments

Andreas Over a year ago

To prevent common newbie mistake, add str = in front.

Andreas Over a year ago

Technically, removing leading spaces is counter to OPs requirements, but it likely makes no difference.

shmosel Over a year ago

@Andreas Where are you seeing that?

Andreas Over a year ago

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 · Accepted Answer · 2017-05-16 20:55:20Z

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.

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