Check if a string is empty or only whitespace in java [duplicate]

Question

So I have a question with my code. A part of my code includes a question for a persons details, and to make sure they answer it correctly. The person cannot answer it blank with whitespace or enter etc. If they answer it incorrectly they're supposed to be sent back to the question again and re-enter their details.

This is how far I've come:

   System.out.println("Name: ");
       String name = scan.nextLine();

   if(name.equals(null) || name.equals("")) {
        System.out.println("Name can't be empty, please enter again.");

   System.out.println("Age: ");
       int age = scan.nextInt();

   if(age.equals(null) || age.equals("")) {
        System.out.println("Age can't be empty, please enter again.");

The thing now is that I'm not quite sure how to handle this if the person answers with whitespace. The code doesn't handle whitespace. Also, how can I make the program automatically go back to ex. "Name:" if it's answered incorrectly?

/Anna

you can call trim before calling equals(""). BTW, you should do name == null otherwise you will end up with a NullPointerException — Lothar
– Lothar, Commented Jan 9, 2018 at 19:55
Copy your question title into Google, and this shows up... How do I check that a Java String is not all whitespaces? — Malte Hartwig
– Malte Hartwig, Commented Jan 9, 2018 at 19:59
Aside from that, you have to change your logic: If the name or the age are empty, you just continue. But instead, you need to scan for them again. You can do this with a while loop. Look at this answer to see how that works. — Malte Hartwig
– Malte Hartwig, Commented Jan 9, 2018 at 20:02
But then again, if the answer is incorrect, how can I write the code so it automatically goes back to "Name: "? — Anna
– Anna, Commented Jan 9, 2018 at 20:24

Alexandre Annic · Accepted Answer · 2018-01-09 20:07:50Z

2

Use trim(). It will removes whitespaces at the start and the end of the string.

if (string.trim().isEmpty())

edited Jan 9, 2018 at 20:07

answered Jan 9, 2018 at 19:56

Alexandre Annic

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5 Comments

Anna Over a year ago

Thank you, tried this but still allows me to enter a name with only whitespace...

Malte Hartwig Over a year ago

@Anna look at my comment on your question.

Alexandre Annic Over a year ago

I tried if (name.equals(null) || name.trim().equals("")) {...}. It works when i entered just spaces.

Ward Over a year ago

Using isEmpty() makes it somewhat more declarative than using length(): !string.trim().isEmpty()

Alexandre Annic Over a year ago

You're right, i edit my answer.

Vladyslav Nikolaiev · Accepted Answer · 2018-01-09 20:11:35Z

1

name.matches("\\s*") will return true is name is empty or spaces only, where name is inputed String

edited Jan 9, 2018 at 20:11

answered Jan 9, 2018 at 20:02

Vladyslav Nikolaiev

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1 Comment

Bohemian Over a year ago

FYI you don't need ^ or $ with java's matches(); they are implied because matches() must match the whole input. You also don't need [ or ]. just name.matches("\\s*") is enough

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