# How to validate CVV number using Regular Expression

Given a string str, the task is to check whether it is a valid CVV (Card Verification Value) number or not by using Regular Expression.
The valid CVV (Card Verification Value) number must satisfy the following conditions:

1. It should have 3 or 4 digit.
2. It should have digit between 0-9.
3. It should not have any alphabets and special characters.

Examples:

Input: str = “561”
Output: true
Explanation:
The given string satisfies all the above mentioned conditions. Therefore it is a valid CVV (Card Verification Value) number.

Input: str = “50614”
Output: false
Explanation:
The given string has five-digit. Therefore it is not a valid CVV (Card Verification Value) number.

Input: str = “5a#1”
Output: false
Explanation: The given string has alphabets and special characters. Therefore it is not a valid CVV (Card Verification Value) number.

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: The idea is to use Regular Expression to solve this problem. The following steps can be followed to compute the answer.

1. Get the String.
2. Create a regular expression to check valid CVV (Card Verification Value) number as mentioned below:
```regex = "^[0-9]{3, 4}\$";
```

Where:

• ^ represents the starting of the string.
• [0-9] represents the digit between 0-9.
• {3, 4} represents the string have 3 or 4 digit.
• \$ represents the ending of the string.
3. Match the given string with the regular expression. In Java, this can be done by using Pattern.matcher().
4. Return true if the string matches with the given regular expression, else return false.

Below is the implementation of the above approach:

 `// Java program to validate ` `// CVV (Card Verification Value) ` `// number using regex. ` `import` `java.util.regex.*; ` `class` `GFG { ` ` `  `    ``// Function to validate ` `    ``// CVV (Card Verification Value) number. ` `    ``// using regular expression. ` `    ``public` `static` `boolean` `    ``isValidCVVNumber(String str) ` `    ``{ ` `        ``// Regex to check valid CVV number. ` `        ``String regex = ``"^[0-9]{3, 4}\$"``; ` ` `  `        ``// Compile the ReGex ` `        ``Pattern p = Pattern.compile(regex); ` ` `  `        ``// If the string is empty ` `        ``// return false ` `        ``if` `(str == ``null``) { ` `            ``return` `false``; ` `        ``} ` ` `  `        ``// Find match between given string ` `        ``// and regular expression ` `        ``// uaing Pattern.matcher() ` ` `  `        ``Matcher m = p.matcher(str); ` ` `  `        ``// Return if the string ` `        ``// matched the ReGex ` `        ``return` `m.matches(); ` `    ``} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `main(String args[]) ` `    ``{ ` ` `  `        ``// Test Case 1: ` `        ``String str1 = ``"561"``; ` `        ``System.out.println( ` `            ``isValidCVVNumber(str1)); ` ` `  `        ``// Test Case 2: ` `        ``String str2 = ``"5061"``; ` `        ``System.out.println( ` `            ``isValidCVVNumber(str2)); ` ` `  `        ``// Test Case 3: ` `        ``String str3 = ``"50614"``; ` `        ``System.out.println( ` `            ``isValidCVVNumber(str3)); ` ` `  `        ``// Test Case 4: ` `        ``String str4 = ``"5a#1"``; ` `        ``System.out.println( ` `            ``isValidCVVNumber(str4)); ` `    ``} ` `} `

Output:

```true
true
false
false
```

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