Check if a String Contains Only Alphabets in Java Using Lambda Expression

Lambda expressions basically express instances of functional interfaces (An interface with a single abstract method is called functional interface. An example is java.lang.Runnable). lambda expressions implement the only abstract function and therefore implement functional interfaces.

Given a String, we just need to iterate over characters again the task is to check whether a string contains only alphabets or not for which primarily we will check edge cases whether the string is present or not and should not be null, we will simply return false as there is no way to deal with that string. When the above condition is not fulfilled we will make use of lambda expression method isLetter() to check for only characters are there or not, and will return a corresponding boolean value. 

Illustrations:

Input : GeeksforGeeks
Output : True

Input  : Geeks4Geeks
Output : False

Input  : null
Output : False

Concept: The idea is to use isLetter() method of Character class. 

Algorithm:

1. Get the string
2. Match the string: 
   • Check if the string is empty or not. If empty, return false
   • Check if the string is null or not. If null, return false.
   • If the string is neither empty nor null, 
     then check using Lambda Expression Character::isLetter().
3. Return true if matched

Pseudocode for the above-proposed algorithm is 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 Lambda Expression

class GFG {

    // Method 1
    // To check String for only Alphabets
    public static boolean isStringOnlyAlphabet(String str)
    {
        return (
            (str != null) && (!str.equals(""))
            && (str.chars().allMatch(Character::isLetter)));
    }

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

        // Calling method over different strings
        // justifying all use-cases possible

        // Display message
        System.out.println("Test Case 1:");

        String str1 = "GeeksforGeeks";
        System.out.println("Input: " + str1);

        // Calling over above string: GeeksforGeeks
        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);

        // Calling over above string: Geeks4Geeks
        System.out.println("Output: "
                           + isStringOnlyAlphabet(str2));

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

        // Calling over above string: null
        System.out.println("Output: "
                           + isStringOnlyAlphabet(str3));

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

        // Calling over above string ""
        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