regEx : Regular Expression to Allow Empty Space with Alphabets and Numbers

The following Java code helps us to allow Empty Space in input keyword/string alongwith the alphabets [a-zA-Z] and numbers [0-9]

The regular expression should be like ^[a-zA-Z0-9 ]+

In this regular expression there is an empty space added before closing bracket ] and a plus sign is added after the same closing bracket ]. The output is returned as true or false

Option-1: Validate the string with the help of Pattern and Matcher classes. Both Pattern and Matcher classes are added since Java 1.4 version.

package com.learning.regex;

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

public class RegexValidationWithPatternMatcher {
	
	public static void main(String[] args) {
		
		String inputString = "Operating System";
		
		Boolean isValidKeyword = validKeyword(inputString);
		
		System.out.println("Is valid keyword : " + isValidKeyword);
		
	}

	
	public static Boolean validKeyword(String keyword) {
        String regex = "^[a-zA-Z0-9 ]+";
        Pattern pattern = Pattern.compile(regex);
        Matcher match = pattern.matcher(keyword);
        return match.matches();
    }

}

The code produces the following output:

Is valid keyword : true

Option-2: Validate the string with String class inbuit matches method which internally calls Pattern.matches() method for given regular expression against the value of String variable. The matcher method is available in String class since Java 1.4 version

package com.learning.regex;

public class RegexValidation {
	
	public static void main(String[] args) {
		
		String inputString = "Operating System";
		
		Boolean isValidKeyword = inputString.matches("^[a-zA-Z0-9 ]+");
		
		System.out.println("Is valid keyword : " + isValidKeyword);
		
	}

}

The code produces the following output:

Is valid keyword : true