CODEWITHSUNDEEP
javastringline-breaks
Max Kleine
Max Kleine

Reputation: 143

Check if String is only line breaks

I am trying to check if a given String contains only line breaks and no characters. I use this method

boolean breaksNoLetters(String msg) {
   if (!msg.matches(".*[a-zA-Z]+.*") && msg.contains("\n")) {
       return true;
   } else {
       return false;
   }
}

It only does not return false if it contains a line break though.

Upvotes: 2

Views: 15136

Answers (5)

Mureinik
Mureinik

Reputation: 310983

One way to go would be to replace \n with a blank string and check if anything remains:

boolean breaksNoLetters(String msg) {
   return !msg.replace("\n", "").isEmpty();
}

EDIT:
With Java 8's streams, it's pretty easy to check that all the characters are, in fact, \ns:

boolean justLineBreaks = msg.chars().allMatch(c -> c == '\n');

Upvotes: 3

springfeld
springfeld

Reputation: 89

Impossible, you wrote

only line breaks and no characters

and line breaks are special character. Step back and think about what problem you want to solve. Is it just to check if a minimum of one single printable character is given? Then trim() the String and check if length() > 0. Else the RegEx above is a good one.

Upvotes: 2

Giulio Biagini
Giulio Biagini

Reputation: 920

If you have to check if a String contains only one line break and no other characters, use the equals() method:

public boolean isLineBreak(String line) {
    return line.equals(System.getProperty("line.separator"));
}

Another suggest I give you, is to use the System.getProperty("line.separator") method in order to get the line separator chars, because it's platform independent. For example, UNIX uses \n and Windows \r\n. With this method you don't have to care of this.

Java 7 has the System.lineSeparator() method, which allows you to do the same as System.getProperty("line.separator").

Otherwise, if you have to check if a String contains one or more line break, simply use this:

public boolean isLineBreak(String line) {
    return line.matches("[\\n\\r]+");
}

Upvotes: 1

Avinash Raj
Avinash Raj

Reputation: 174696

I am trying to check if a given String contains only line breaks and no characters.

String Path1 = "\n\r";
String Path2 = "foo\nbar";
System.out.println(Path1.matches("[\\n\\r]+"));
System.out.println(Path2.matches("[\\n\\r]+"));

"[\\n\\r]+" matches one or more new line or carriage return characters. Use also the \\f (form feed) inside the character class if necessary.

Output:

true
false

Upvotes: 6

Konstantin Yovkov
Konstantin Yovkov

Reputation: 62854

Why not test it against this regex?

if (msg.matches("[\\n\\r]+")) { }

This regular expression will match all the strings that contain one or more characters from the set of \n and \r.

Upvotes: 12

Related Questions