Gmail Validation in Python and Java (Without Using Predefined Methods)

Introduction

Validating user input is an important concept in programming, especially for login and registration systems. One common task is checking whether an email (Gmail) is valid.

In this blog, we will learn how to validate a Gmail address using:

• Python
• Java

And the important part: without using advanced predefined methods like regex

---

Problem Statement

We need to check:

• Only valid characters are used
• Email ends with @gmail.com

---

Python Implementation

```python id="8y2b2a"
def verify_Gmail(Gmail):
i = 0
while i < len(Gmail):
current = Gmail[i]
i += 1

    if current >= "a" and current <= "z":
        continue
    elif current >= "A" and current <= "Z":
        continue
    elif current >= "0" and current <= "9":
        continue
    elif current == "@" or current == "." or current == "_":
        continue
    else:
        return False

if Gmail[-10:] == "@gmail.com":
    return True
else:
    return False

if verify_Gmail(input("Enter Your Gmail :")):
print("valid")
else:
print("invalid")

---

##  Java Implementation



```java id="0m5x2r"
import java.util.*;

public class GmailValidation {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        System.out.print("Enter Your Gmail: ");
        String Gmail = sc.nextLine();

        if (verifyGmail(Gmail)) {
            System.out.println("valid");
        } else {
            System.out.println("invalid");
        }

        sc.close();
    }

    public static boolean verifyGmail(String Gmail) {

        // Check each character
        for (int i = 0; i < Gmail.length(); i++) {
            char current = Gmail.charAt(i);

            if (current >= 'a' && current <= 'z') {
                continue;
            } else if (current >= 'A' && current <= 'Z') {
                continue;
            } else if (current >= '0' && current <= '9') {
                continue;
            } else if (current == '@' || current == '.' || current == '_') {
                continue;
            } else {
                return false;
            }
        }

        // Check ending "@gmail.com"
        if (Gmail.length() >= 10) {
            String lastPart = Gmail.substring(Gmail.length() - 10);
            if (lastPart.equals("@gmail.com")) {
                return true;
            }
        }

        return false;
    }
}

---

Logic Explanation

Step 1: Loop through each character

We check every character using:

• Python → while loop
• Java → for loop

---

Step 2: Validate allowed characters

Allowed:

• Alphabets (a–z, A–Z)
• Numbers (0–9)
• Special characters: @, ., _

If any other character appears → invalid

---

Step 3: Check Gmail domain

We ensure the email ends with:

```text id="bh84jm"
@gmail.com

---

##  Valid Examples

* `[e-mail]`
* `[e-mail]`

---

##  Invalid Examples

* `ponvel@gmail` 
* `ponvel#@gmail.com` 
* `[e-mail]` 

---

##  Limitations

* Does not check multiple `@` symbols
* Does not fully validate email format
* Basic validation only