How to check whether a String contains '\r' \t' '\n'...other than spaces

Question

How to check whether a String contains all '\r' \t' '\n'...other than spaces?

For example, String a = "a\nb", String b = "a b". I want return true for string a, false for string b.

I know there is Character.isWhiteSpace(char c), and Pattern.compile("\\s").matcher(string).find(). But they all take space(' ') into account. What I want is find out all escape characters which is considered as whitespace by Character.isWhiteSpace(char c) method except for ' '.

And I don't want to check char by char, it will be the best if there is a proper regex and I can use like Pattern.compile.

@antoni because I want to find out all whitespace defined by Character.isWhitespace(char) other than space itself. I think except for \n|\r|\t, there must be more escape characters that Character.isWhitespace(char) defines as whitespace — yunjing li, Dec 29 '16 at 17:39

score 3 · Answer 1 · answered Dec 29 '16 at 01:46

3

Like this?

@Test
    public void testLines() {
        assertTrue(Pattern.compile("[\n\r\t]").matcher("a\nb").find());
        assertFalse(Pattern.compile("[\n\r\t]").matcher("a b").find());
    }

answered Dec 29 '16 at 01:46

Jochen Bedersdorfer

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score 2 · Accepted Answer · answered Dec 29 '16 at 01:47

2

You could use [^\S ] which matches everything but \S (non-whitespace) or (space).

Pattern pattern = Pattern.compile("[^\\S ]");

String a = "a\nb";
String b = "a b";

System.out.println(pattern.matcher(a).find()); // true
System.out.println(pattern.matcher(b).find()); // false

answered Dec 29 '16 at 01:47

Bubletan

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Thanks! That's what I'm looking for :) – yunjing li Dec 29 '16 at 17:46

score 1 · Answer 3 · edited May 23 '17 at 12:25

I assume that when you say "all '\r' \t' '\n'...other than spaces", what you mean is "any whitespace character other than U+0020" (where U+0020 is a simple space). Is this correct?

If so, then the following regex (general form) should work:

(?! )\s

This will match any whitespace character that is not a simple space. This regex makes use of negative lookahead.

EDIT:

As @Bubletan states in their answer, the following regex will also work:

[^\S ]

Both of these regex are equivalent. This is because (?! )\s ≣ "(is NOT the character U+0020) AND (is whitespace)" and [^\S ] ≣ "is NOT (non-whitespace OR the character U+0020) have the same truth table:

Let P(x) be the predicate "x is the character U+0020"
Let Q(x) be the predicate "x is whitespace"

P | Q | (¬P)∧Q | ¬(¬Q∨P)
–– ––– –––––––– ––––––––
T   T      F       F
T   F      T       T
F   T      F       F
F   F      F       F

Although for the sake of efficiency, you are probably better off using @Bubletan's solution ([^\S ]). Lookaround is generally slower than the alternative.

This is how you could implement it:

// Create the pattern.  (do only once)
Pattern pattern = Pattern.compile("[^\\S ]");

// Test an input string.  (do for each input)
Matcher matcher = pattern.matcher(string);
boolean result = matcher.find();

result will then indicate whether string contains any whitespace other than a simple space.

That's a very detailed answer! Thanks! – yunjing li Dec 29 '16 at 17:47 — yunjing li, Dec 29 '16 at 17:47

score 0 · Answer 4 · answered Dec 29 '16 at 02:55

0

In Java, use [^\\h]+ . \h means all kinds of horizontal spaces. But in other languages, it is not available as far as I know.

answered Dec 29 '16 at 02:55

Kang Andrew

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How to check whether a String contains '\r' \t' '\n'...other than spaces

4 Answers4

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