How do I use a delimiter with Scanner.useDelimiter in Java?

Question

sc = new Scanner(new File(dataFile));
sc.useDelimiter(",|\r\n");

I don't understand how delimiter works, can someone explain this in layman terms?

Solution 1

The scanner can also use delimiters other than whitespace.

Easy example from Scanner API:

 String input = "1 fish 2 fish red fish blue fish";

 // \\s* means 0 or more repetitions of any whitespace character 
 // fish is the pattern to find
 Scanner s = new Scanner(input).useDelimiter("\\s*fish\\s*");

 System.out.println(s.nextInt());   // prints: 1
 System.out.println(s.nextInt());   // prints: 2
 System.out.println(s.next());      // prints: red
 System.out.println(s.next());      // prints: blue

 // don't forget to close the scanner!!
 s.close(); 

The point is to understand the regular expressions (regex) inside the Scanner::useDelimiter. Find an useDelimiter tutorial here.

---

To start with regular expressions here you can find a nice tutorial.

Notes

abc…    Letters
123…    Digits
\d      Any Digit
\D      Any Non-digit character
.       Any Character
\.      Period
[abc]   Only a, b, or c
[^abc]  Not a, b, nor c
[a-z]   Characters a to z
[0-9]   Numbers 0 to 9
\w      Any Alphanumeric character
\W      Any Non-alphanumeric character
{m}     m Repetitions
{m,n}   m to n Repetitions
*       Zero or more repetitions
+       One or more repetitions
?       Optional character
\s      Any Whitespace
\S      Any Non-whitespace character
^…$     Starts and ends
(…)     Capture Group
(a(bc)) Capture Sub-group
(.*)    Capture all
(ab|cd) Matches ab or cd

Solution 2

With Scanner the default delimiters are the whitespace characters.

But Scanner can define where a token starts and ends based on a set of delimiter, wich could be specified in two ways:

1. Using the Scanner method: useDelimiter(String pattern)
2. Using the Scanner method : useDelimiter(Pattern pattern) where Pattern is a regular expression that specifies the delimiter set.

So useDelimiter() methods are used to tokenize the Scanner input, and behave like StringTokenizer class, take a look at these tutorials for further information:

• Setting Delimiters for Scanner
• Java.util.Scanner.useDelimiter() Method

And here is an Example:

public static void main(String[] args) {

    // Initialize Scanner object
    Scanner scan = new Scanner("Anna Mills/Female/18");
    // initialize the string delimiter
    scan.useDelimiter("/");
    // Printing the tokenized Strings
    while(scan.hasNext()){
        System.out.println(scan.next());
    }
    // closing the scanner stream
    scan.close();
}

Prints this output:

Anna Mills
Female
18

Solution 3

For example:

String myInput = null;
Scanner myscan = new Scanner(System.in).useDelimiter("\\n");
System.out.println("Enter your input: ");
myInput = myscan.next();
System.out.println(myInput);

This will let you use Enter as a delimiter.

Thus, if you input:

Hello world (ENTER)

it will print 'Hello World'.

Comments

[georges]

just fyi: this line: Scanner s = new Scanner(input).useDelimiter("\\sfish\\s"); actually has a resource leak, even if you call s.close(). The leak is on the scanner that useDelimiter is called on. If you instead call Scanner s = new Scanner(input); s.useDelimiter(\\s*fish\\s); you avoid this problem.

[Jordi Castilla]

@georges actually my line is: ("\\sfish\\s")... not ("\\sfish\\s") but can you please clarify what you mean?

[DSlomer64]

In other words, to a novice this Answer and comments is no help whatsoever to NoMoreErrors. Learn regex just to use Scanner?????? Sure, it would help, but it's waaaaaaay past what he needs. Just give an example. Simple friggin' example.

[DSlomer64]

Yeah, but how does it work? What are TWO backslashes for? But hooray, now we know how to use Enter as a delimiter. Assuming it works.

[Jordi Castilla]

@DSlomer64 actuallty you don't need regex to use Scanner but if you want to use your custom delimiter is mandatory to use regex because is what useDelimiter method accepts as input. This is what OP asked and as long as is the accepted as answer, IMHO it suits OP. Why you think OP is a novice? If being a novice it's your case and the answer does not fit you please ask a new question :)

[DSlomer64]

@JordiCastilla--OP is almost definitely a novice because of the level of his question and rep 353. So his useDelimiter example certainly needs explaining, My point was that we need to factor in user's experience and actual need and not go off on a tangent (from user's point of view) but you've made me realize this: the user can quit reading comments once he's in too deep or continue reading to learn more.I was reading too much from OP's mind. Your point is well taken. :^}