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
- Get the string
- Match the string with the Regex using matches().
- 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]*$"))); }
Example:
// Java Program to Check If String Contains Only Alphabets // Using Regular Expression // Main class class GFG {
// Method 1
// To check String for only Alphabets
public static boolean isStringOnlyAlphabet(String str)
{
return ((str != null ) && (!str.equals( "" ))
&& (str.matches( "^[a-zA-Z]*$" )));
}
// 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));
}
} |
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
Related Articles:
- Check if a string contains only alphabets in Java using ASCII values
- Check if a string contains only alphabets in Java using Lambda expression