JAVA EE: How to create a regex that accepts alphanumeric characters and length is 4

Thursday 30 November 2017

Click here to watch in Youtube :
https://www.youtube.com/watch?v=aGo-W_vIfx0&list=UUhwKlOVR041tngjerWxVccw

RegexDemo.java

import java.util.regex.Pattern;

/**
 *
 * Create a regular expression that accepts alpha numeric characters only. Its
 * length must be 4 characters long only.
 *
 */

public class RegexDemo
{
    public static void main(String[] args)
    {
        /*
         * Parameters:
         * 
         * regex - The expression to be compiled
         * 
         * input - The character sequence to be matched
         * 
         * Returns:
         * 
         * whether or not the regular expression matches on the input
         * 
         */
        System.out.println(Pattern.matches("[a-zA-Z0-9]{4}", "Juli"));//true
        System.out.println(Pattern.matches("[a-zA-Z0-9]{4}", "Ju22"));//true
        System.out.println(Pattern.matches("[a-zA-Z0-9]{4}", "Peter"));//false (more than 4 char)
        System.out.println(Pattern.matches("[a-zA-Z0-9]{4}", "J$22"));//false ($ is not matched)
    }

}