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

Examples:

Input: PrutordotAi
Output: True

Input: Prutor4Prutor
Output: False

Input: null
Output: False

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 P_AI {

// 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 = "PrutordotAi";
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 = "Prutor4Prutor";
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: PrutordotAi
Output: true

Test Case 2:
Input: Prutor4Prutor
Output: false

Test Case 3:
Input: null
Output: false

Test Case 4:
Input:
Output: false