regex for string checking for not null [closed]

Question

I need a Java regular expression, which checks that the given String is not Empty and not null . However the expression should ingnore if the user has accidentally given whitespace in the beginning of the input, but allow whitespaces later on.

"ignore" whitespace at the beginning: does that mean " " and " test" fail or pass validation? — Evan Davis
– Evan Davis, Commented Apr 10, 2012 at 13:10
You cannot check for a null reference with a regular expression in Java. You must separately check that the reference is not null then compare the string with a regular expression. — maerics
– maerics, Commented Apr 10, 2012 at 13:11
@maerics thank you but the thing is that my boss told me to dat using regex only how can i explain him — user1324126
– user1324126, Commented Apr 10, 2012 at 13:12
your boss told you to do this? I recommend going to careers.stackoverflow.com and submitting a resume. — Woot4Moo
– Woot4Moo, Commented Apr 10, 2012 at 13:14
To perform a regalur expression check you need to have a String to check. null is not a String object. — Peter Lawrey
– Peter Lawrey, Commented Apr 10, 2012 at 13:14

fqsxr · Accepted Answer · 2012-04-10 13:09:52Z

8

You could do it without using regex.

boolean check(String s) {
  return s != null && s.trim().length() > 0;
}

answered Apr 10, 2012 at 13:09

fqsxr

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2 Comments

Woot4Moo Over a year ago

@user1324126 that is a terrible idea.

Travis Crum Over a year ago

@Woot4Moo its not a good idea but still necessary for certain things

Anonymous · Accepted Answer · 2012-04-10 13:10:30Z

3

You can use Guava to check for nullity and emptiness:

Strings.isNullOrEmpty(myString);

And you cannot use regular expressions on a null String.

answered Apr 10, 2012 at 13:10

Anonymous

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Comments

Alex Stybaev · Accepted Answer · 2012-04-10 13:10:38Z

2

Try this:

yourString != null && yourString.trim().length() > 0

answered Apr 10, 2012 at 13:10

Alex Stybaev

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Comments

maerics · Accepted Answer · 2012-04-10 13:13:55Z

0

You cannot check for a null reference with a regular expression in Java. You must separately check that the reference is not null then compare the string with a regular expression.

public static boolean isNullEmptyOrWhitespace(String s) {
  return (s==null) || s.matches("^\\s*$");
}

answered Apr 10, 2012 at 13:13

maerics

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