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?

Answer 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.

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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 

Answer 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