How to Check That a Java String Is Not All Whitespaces

How do I check that a Java String is not all whitespaces?

Shortest solution I can think of:

if (string.trim().length() > 0) ...

This only checks for (non) white space. If you want to check for particular character classes, you need to use the mighty match() with a regexp such as:

if (string.matches(".*\\w.*")) ...

...which checks for at least one (ASCII) alphanumeric character.

How do I check whether input string contains any spaces?

Why use a regex?

name.contains(" ")

That should work just as well, and be faster.

How to detect string which contains only spaces?

To achieve this you can use a Regular Expression to remove all the whitespace in the string. If the length of the resulting string is 0, then you can be sure the original only contained whitespace. Try this:

var str = "    ";if (!str.replace(/\s/g, '').length) {  console.log('string only contains whitespace (ie. spaces, tabs or line breaks)');}

How can I check if string contains characters & whitespace, not just whitespace?

Instead of checking the entire string to see if there's only whitespace, just check to see if there's at least one character of non whitespace:

if (/\S/.test(myString)) {
    // string is not empty and not just whitespace
}

How can I find whitespace in a String?

For checking if a string contains whitespace use a Matcher and call its find method.

Pattern pattern = Pattern.compile("\\s");
Matcher matcher = pattern.matcher(s);
boolean found = matcher.find();

If you want to check if it only consists of whitespace then you can use String.matches:

boolean isWhitespace = s.matches("^\\s*$");

Checking if there is whitespace between two elements in a String

You would use String.strip() to remove any leading or trailing whitespace, followed by String.split(). If there is a whitespace, the array will be of length 2 or greater. If there is not, it will be of length 1.

Example:

String test = "    2 2   ";
test = test.strip(); // Removes whitespace, test is now "2 2"
String[] testSplit = test.split(" "); // Splits the string, testSplit is ["2", "2"]
if (testSplit.length >= 2) {
    System.out.println("There is whitespace!");
} else {
    System.out.println("There is no whitespace");
}

If you need an array of a specified length, you can also specify a limit to split. For example:

"a b c".split(" ", 2); // Returns ["a", "b c"]

If you want a solution that only uses regex, the following regex matches any two groups of characters separated by a single space, with any amount of leading or trailing whitespace:

\s*(\S+\s\S+)\s*

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