How do I use a delimiter in Java Scanner?

问题

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

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

回答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

回答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

回答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'.

来源：https://stackoverflow.com/questions/28766377/how-do-i-use-a-delimiter-in-java-scanner