java regular expression for multiple spaces

Question

Can I write a single line regular expression instead of the five lines below?

strTestIn = strTestIn.replaceAll("^\\s+", "");
strTestIn = strTestIn.replaceAll("[ ]+", " ");
strTestIn = strTestIn.replaceAll("(\\r\\n)+", "\r\n");
strTestIn = strTestIn.replaceAll("(\\t)+", " ");
strTestIn = strTestIn.replaceAll("\\s+$", "");

What's the difference between these regular expressions?

Answer 1

strTestIn = strTestIn.replaceAll("^\\s+", "");

removes whitespace at the start of the string.

strTestIn = strTestIn.replaceAll("\\s+$", "");

removes whitespace at the end of the string.

strTestIn = strTestIn.replaceAll("[ ]+", " ");

condenses multiple spaces into a single space.

strTestIn =strTestIn.replaceAll("(\\r\\n)+", "\r\n");

removes empty lines by replacing adjacent newlines with a single newline.

strTestIn = strTestIn.replaceAll("(\\t)+", " ");

condenses tabs into a single space.

So they all do different things. A combination is possible for those that have the same replacement string:

strTestIn = strTestIn.replaceAll("^\\s+|\\s+$", "");
strTestIn = strTestIn.replaceAll(" {2,}|\t+", " ");
strTestIn = strTestIn.replaceAll("(\r\n)+", "\r\n");

You can also clean up and improve the regexes a bit (removing some unnecessary backslashes, and changing the minimum number of spaces to two).