What are the uses of regular expressions in java

Java regular expressions are used for text manipulation tasks, including validating input (such as email addresses), extracting data (such as integers), replacing text, splitting strings, finding matches, and creating custom matchers.

Usage of Java regular expressions

Regular expressions (regex) are powerful pattern matching tools. It can be used for various text manipulation tasks in Java. Its usage is extensive, including:

1. Verify input

• Verify email address: String email = "example@example.com"; boolean isValid = email.matches("^[a-zA-Z0-9.!#$%&'* /=?^_{|}~-] @[a-zA-Z0-9]( ?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA- Z0-9-]{0,61}[a-zA-Z0-9])?)*$");`

2. Extract data

• Extract integers from strings: String text = "The number is 123"; int number = Integer.parseInt(text.replaceAll("[^\\d]", "")) ;

3. Replace text

• Replace all numbers in the string with X: String text = "123abc456 "; text = text.replaceAll("[0-9]", "X");

4. Split the string

• Split the string by commas: String[] tokens = text.split(",");

5. Find matches

• Find lines in a string that begin with a specific pattern: List<String> matches = Files.lines(Paths.get("file.txt")).filter(line -> line.startsWith("PATTERN")).toList();

#6. Custom matcher

• Create custom Matcher to validate a specific format: Predicate<String> isPhoneNumber = Pattern.matches("^\\(\\d{3}\\) \\d{3}-\\d{4}$") ;

Syntax

The regular expression syntax is based on the following notation:

• Normal characters: Matches itself
• Escape characters: Escape the meaning of special characters
• Modifier: Specify the matching behavior
• Quantifier: Specify the number of matches

Use Tip

• Consider using a regular expression library (such as Apache Commons Regex) to simplify complex patterns.
• Test the regular expression to make sure it works as expected.
• Use appropriate boundary anchors to avoid accidental matches.
• Avoid overuse of regular expressions as they can be inefficient.

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