Java Regular Expressions – 1

What is Java Regular Expressions?

From Oracle, it says “Regular expressions are a way to describe a set of strings based on common characteristics shared by each string in the set.” In order to define that common characteristics, we prepare a sequence of characters called ‘Pattern’. These patterns can be used to search, edit, or manipulate text and data.

java.util.regex API

The regular expression syntax in the java.util.regex API which consists of three classes: Pattern, Matcher, and PatternSyntaxException.

Pattern

• A Pattern object is a compiled representation of a regular expression.
• The Pattern class provides no public constructors.
• To create a pattern, you must first invoke one of its public static compile() methods, which will then return a Pattern object.
• These methods accept a regular expression as the first argument; the following sections are covering the required syntax.

Matcher

• A Matcher object is the engine that interprets the pattern and performs match operations against an input string.
• Like the Pattern class, Matcher defines no public constructors.
• You obtain a Matcher object by invoking the matcher() method on a Pattern object

PatternSyntaxException

• A PatternSyntaxException object is an unchecked exception that indicates a syntax error in a regular expression pattern.

Demo

package com.bruiser.regexp;

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

public class RegExp {

	public static void main(String[] args) {
		String searchPattern = "Tech";
		String inputString = "Welcome To TechBruiser!";
		Pattern pattern = Pattern.compile(searchPattern);
		Matcher matcher = pattern.matcher(inputString);		
		boolean matchFound = matcher.find();
		if(matchFound) {
			System.out.printf("The search pattern '%s' is available in input '%s' ", searchPattern, inputString);
		}else {
			System.out.printf("Match no found");

		}		
	}
}

The search pattern 'Tech' is available in input 'Welcome To TechBruiser!'

Great. Now we know about java regular expressions. But is that all about regular expressions ? No way. it is just a kickstart. Let’s move on to the next session to get most out of regular expression.