Check if a string contains only alphabets in Java using Regex

Difficulty Level : Easy
Last Updated : 03 Feb, 2020

Given a string, the task is to check whether a string contains only alphabets or not using Regex in Java.

Examples:

Input: GeeksforGeeks
Output: True

Input: Geeks4Geeks
Output: False

Input: null
Output: False

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

In this article, the characters of the string are checked one by one 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.

The Regex

^[a-zA-Z]*$

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.

Algorithm:

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

Pseudocode:

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

Below is the implementation of the above approach:

Program: Checking for String containing only Alphabets

// Java program to check if String contains only Alphabets
// using Regular Expression
  
class GFG {
  
    // Function to check String for only Alphabets
    public static boolean isStringOnlyAlphabet(String str)
    {
        return ((str != null)
                && (!str.equals(""))
                && (str.matches("^[a-zA-Z]*$")));
    }
  
    // Main method
    public static void main(String[] args)
    {
  
        // Checking for True case
        System.out.println("Test Case 1:");
  
        String str1 = "GeeksforGeeks";
        System.out.println("Input: " + str1);
        System.out.println(
            "Output: "
            + isStringOnlyAlphabet(str1));
  
        // Checking for String with numeric characters
        System.out.println("\nTest Case 2:");
  
        String str2 = "Geeks4Geeks";
        System.out.println("Input: " + str2);
        System.out.println(
            "Output: "
            + isStringOnlyAlphabet(str2));
  
        // Checking for null String
        System.out.println("\nTest Case 3:");
  
        String str3 = null;
        System.out.println("Input: " + str3);
        System.out.println(
            "Output: "
            + isStringOnlyAlphabet(str3));
  
        // Checking for empty String
        System.out.println("\nTest Case 4:");
  
        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

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