Regular Expressions

• Regex means a Regular Expression
• It is a search pattern which is formed by a sequence of characters
• Used to search patterns in a string
• To use Regex class we need to import java.util.regex

Methods in java.util.regex

1. Pattern

• Defines a pattern that is to be searched
• A pattern is created using the function compile()
• It has 2 parameters, First parameter used to indicate the pattern that is searched and the other parameter is a flag to tell the case-sensitivity

Patterns

• [xyz] : Finds a character from options between the brackets
• [^xyz] : Finds a character from options not between the brackets

Flags

• pattern.LITERAL : special characters also treated as normal characters
• pattern.CASE_INSENSITIVE : case of letters is not considered

2. Matcher

Used to search the patterns

3. PatternSyntaxException

Used to tell syntax error in a regex pattern

Example

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Main {
  public static void main(String[] args) {
    Pattern pattern = Pattern.compile("onecompiler", Pattern.CASE_INSENSITIVE);
    Matcher matcher = pattern.matcher("Welcome to onecompiler");
    boolean search = matcher.find();
    if(search) {
      System.out.println("found");
    } else {
      System.out.println("Not found");
    }
  }
}

check output here