Check if line is empty in java?

Question

Possible Duplicate:
How to check that Java String is not all whitespaces

Scanner kb = new Scanner(System.in);
String random;

System.out.print("Enter your word: ");
random = kb.nextLine();

if (random.isEmpty()) {     
    System.out.println("No input detected!");                   
} else {
    System.out.println(random);
}

The above code doesn't account for when the user makes a space. It'll still print the blank line, when the user does a space and presses enter.

How do I fix this?

This question has been asked [so](http://stackoverflow.com/q/3824438/851811) [many](http://stackoverflow.com/q/14625265/851811) [times](http://stackoverflow.com/q/3247067/851811). — Xavi López, Feb 04 '13 at 15:48

Rohit Jain · Accepted Answer · 2013-02-04T15:51:06.713

21

You can trim the whitespaces using String#trim() method, and then do the test: -

if (random.trim().isEmpty())

edited Feb 04 '13 at 15:51

answered Feb 04 '13 at 15:44

Rohit Jain

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1

+1 trim() trims characters less than or equal to space. This means it removes control characters which are not whitespace and doesn't remove some characters which are. ;) – Peter Lawrey Feb 04 '13 at 15:47
2

FYI `for(int i=0;i – Peter Lawrey Feb 04 '13 at 15:48
@PeterLawrey. o.O. That is something new to me. Haven't come accross `MAX_CODE_POINT` constant before. What is it? Will take a look. – Rohit Jain Feb 04 '13 at 15:50
@PeterLawrey.. That is really a useful information I got to know today. thanks. I think, I should visit the documentations more often. :) – Rohit Jain Feb 04 '13 at 15:53
The maximum `int` character you can have, called a code point. > 65535. It should be `<=` not `<` – Peter Lawrey Feb 04 '13 at 15:53

score 3 · Answer 2 · answered Feb 04 '13 at 15:45

3

Another solution could be trim and equals with empty string.

if (random.trim().equals("")){       
            System.out.println("No input detected!");                   
}

answered Feb 04 '13 at 15:45

Subhrajyoti Majumder

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you would rather do "".equals(random.trim()) so that a null random doesn't throw a NPE. in that case, your solution would be more robust than rohit jains, which doesn't check for nulls. – Dhruv Gairola Feb 04 '13 at 15:46
2

I think then also it should give NPE on `random.trim()` – Subhrajyoti Majumder Feb 04 '13 at 15:48
oh yeah, didn't notice that. – Dhruv Gairola Feb 04 '13 at 15:49

score 1 · Answer 3 · edited Feb 04 '13 at 15:52

1

another solution

if (random != null || !random.trim().equals(""))
   <br>System.out.println(random);
<br>else
   <br>System.out.println("No input detected!");

edited Feb 04 '13 at 15:52

PermGenError

45,977
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answered Feb 04 '13 at 15:51

M.Kreusburg

19
6

Xavi López · Answer 4 · 2015-07-08T07:29:55.720

1

This is how Apache Commons does it:

public static boolean isBlank(String str) {
    int strLen;
    if (str == null || (strLen = str.length()) == 0) {
        return true;
    }
    for (int i = 0; i < strLen; i++) {
        if ((Character.isWhitespace(str.charAt(i)) == false)) {
            return false;
        }
    }
    return true;
}

edited Jul 08 '15 at 07:29

answered Feb 04 '13 at 15:54

Xavi López

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Check if line is empty in java?

4 Answers4