Check if a String Contains only Alphabets in Java using Regex

Regular Expressions or Regex is an API for defining String patterns that can be used for searching, manipulating, and editing a text. It is widely used to define a constraint on strings such as a password. Regular Expressions are provided under java.util.regex package.

For any string, here the task is to check whether a string contains only alphabets or not using Regex. Now for a given string, the characters of the string are checked one by one using Regex. Regex can be used to check a string for alphabets. String.matches() method is used to check whether or not the string matches the given regex.

^[a-zA-Z]*$

Illustrations:

Input: GeeksforGeeks
Output: True

Input: Geeks4Geeks
Output: False

Input: null
Output: False

Algorithm

1. Get the string
2. Match the string with the Regex using matches().
3. Return true is matched

Pseudocode for the above algorithm is proposed below as follows:

public static boolean isStringOnlyAlphabet(String str) 
{
    return ((!str.equals(""))
            && (str != null)
            && (str.matches("^[a-zA-Z]*$")));
}

Example:

Java

// Java Program to Check If String Contains Only Alphabets
// Using Regular Expression

// Main class
class GFG {

    // Method 1
    // To check String for only Alphabets
    public static boolean isStringOnlyAlphabet(String str)
    {

        return ((str != null) && (!str.equals(""))
                && (str.matches("^[a-zA-Z]*$")));
    }

    // Method 2
    // Main driver method
    public static void main(String[] args)
    {

        // Calling out methods over string
        // covering all scenarios

        // Use case 1
        System.out.println("Test Case 1:");
        // Input string
        String str1 = "GeeksforGeeks";
        System.out.println("Input: " + str1);

        System.out.println("Output: "
                           + isStringOnlyAlphabet(str1));

        // Use case 2
        // Checking for String with numeric characters
        System.out.println("\nTest Case 2:");
        // Input string
        String str2 = "Geeks4Geeks";
        System.out.println("Input: " + str2);
        System.out.println("Output: "
                           + isStringOnlyAlphabet(str2));

        // Use Case 3
        // Checking for null String
        System.out.println("\nTest Case 3:");
        // Input string
        String str3 = null;
        System.out.println("Input: " + str3);
        System.out.println("Output: "
                           + isStringOnlyAlphabet(str3));

        // Use Case 4
        // Checking for empty String
        System.out.println("\nTest Case 4:");
        // Input string
        String str4 = "";
        System.out.println("Input: " + str4);
        System.out.println("Output: "
                           + isStringOnlyAlphabet(str4));
    }
}

Output:

Test Case 1:
Input: GeeksforGeeks
Output: true

Test Case 2:
Input: Geeks4Geeks
Output: false

Test Case 3:
Input: null
Output: false

Test Case 4:
Input: 
Output: false