Real World Example

When you sign up on an app such as Zomato or LinkedIn, the backend cleans and validates the text you typed. String methods do most of that work.

Example

public class Main {
    public static void main(String[] args) {
        String name = "  priya sharma ";
        String email = " [email protected]";
        String phone = "98765-43210";
        String password = "secret";

        String cleanName = name.trim();
        cleanName = cleanName.substring(0, 1).toUpperCase() + cleanName.substring(1);
        String cleanEmail = email.trim().toLowerCase();
        String cleanPhone = phone.replace("-", "");

        System.out.println("Name     : " + cleanName);
        System.out.println("Email    : " + cleanEmail);
        System.out.println("Phone    : " + cleanPhone);

        boolean emailOk = cleanEmail.contains("@") && cleanEmail.indexOf('.') > 0;
        boolean phoneOk = cleanPhone.length() == 10 && cleanPhone.chars().allMatch(Character::isDigit);
        boolean passwordOk = password.length() >= 8;

        System.out.println("Email valid    : " + emailOk);
        System.out.println("Phone valid    : " + phoneOk);
        System.out.println("Password valid : " + passwordOk + (passwordOk ? "" : " (min 8 characters)"));
        System.out.println("Masked phone   : " + "*".repeat(6) + cleanPhone.substring(6));
    }
}

Output

Name     : Priya sharma
Email    : [email protected]
Phone    : 9876543210
Email valid    : true
Phone valid    : true
Password valid : false (min 8 characters)
Masked phone   : ******3210

Signup Form Validation

Example