How Can Java\'s `Scanner.useDelimiter()` Be Used with Regular Expressions to Split Input?

Understanding Scanner.useDelimiter with Regular Expressions

In Java's Scanner API, the useDelimiter() method allows you to specify a delimiter to split the input text into tokens. However, delimiters other than whitespace can be used, requiring the understanding of regular expressions (regex) patterns.

Regex Patterns in useDelimiter()

To use a delimiter with useDelimiter(), you need to provide a regex pattern. This pattern defines the characters or sequences that should separate the tokens.

For example, the code snippet below uses the delimiter "|,|rn" to split the input based on commas (",") or new lines (rn):

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

This means that the scanner will treat commas and new lines as separators, splitting the input into tokens.

Examples

To illustrate how useDelimiter() works with regex patterns, consider the following example:

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

// Use "\s*fish\s*" as the delimiter to split the input
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

Here, the delimiter "sfishs" matches 0 or more repetitions of whitespace characters ("s*") followed by the word "fish" and again 0 or more repetitions of whitespace. As a result, the input is split into tokens based on the delimiter, and the scanner can extract the desired values.

Additional Resources

For more information on useDelimiter() and regex patterns, refer to the following resources:

• Scanner API: https://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html
• Regex Tutorial: https://www.vogella.com/tutorials/JavaRegularExpressions/article.html
• Regex Quick Reference: https://www.regular-expressions.info/quickref.html

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