Regular Expressions Basics

Part of the Logic & Flow section of Coddy's Java journey. Lesson 46 of 59.

Regular Expressions (regex) are patterns used to search and validate strings. In Java, we use the matches() method to check if a string matches a pattern.

Check if a string contains only digits:

String text = "12345";
boolean isMatch = text.matches("[0-9]+");

After executing the above code, isMatch contains:

true

Check if a string contains only letters:

String text = "Hello";
boolean isMatch = text.matches("[a-zA-Z]+");

After executing the above code, isMatch contains:

true

Challenge

Easy

Create a method named validateInput that takes two arguments:

A String (text) to validate
A String (type) that specifies the validation type

The method should validate the text based on these types:

"number": must contain only digits (0-9)
"word": must contain only letters (a-z or A-Z)
"email": must contain @ and at least one character before it
"phone": must contain exactly 10 digits

Return messages should be:

If text is null: return "Invalid input"
If type is invalid: return "Invalid type"
If validation passes: return "Valid"
If validation fails: return "Invalid"

Try it yourself

import java.util.Scanner;

public class Main {
    public static String validateInput(String text, String type) {
        // Write your code here
    }
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String text = scanner.nextLine();
        String type = scanner.nextLine();
        
        if (text.equals("null")) text = null;
        System.out.println(validateInput(text, type));
    }
}