Wap to Reverse a String in Java using Lambda Expression

In Java, a String is a sequence of characters that remains immutable once created. If there's a need to reverse a user-entered string, the `charAt()` method from the String class can be employed. The method facilitates the extraction of individual characters from the string, enabling their concatenation in reverse order to achieve the desired reversal.

Moreover, the Stream API, coupled with Lambda Expressions, offers a functional and declarative means of data manipulation in Java. To reverse a String using Lambda Expressions, the common procedure entails converting the String into a character stream, implementing the reversal operation, and subsequently converting it back into a String.

Example 1

Filename: StringLambdaExample1.java

import java.util.Scanner;

// Define a functional interface for string operations
interface StringFunction {
    String reverse(String input);
}

// Main class to demonstrate string reversal using lambda expressions
public class StringLambdaExample1 {
    public static void main(String[] args) {
        // Create a Scanner object for user input
        Scanner scanner = new Scanner(System.in);

        // Lambda expression for string reversal
        StringFunction reverseFunction = (str) -> {
            // Initialize an empty string to store the reversed result
            String reversedString = "";

            // Iterate through the characters of the input string in reverse order
            for (int index = str.length() - 1; index >= 0; index--) {
                // Append each character to the reversed string
                reversedString += str.charAt(index);
            }

            // Return the reversed string
            return reversedString;
        };
        // Example using a fixed string
        String fixedString = " javaTpoint";
        System.out.println("Reversed word using lambda function: " + reverseFunction.reverse(fixedString));
        // Input from the user
        System.out.println("Enter a string to be reversed:");
        String userInput = scanner.nextLine();
        System.out.println("After reversing: " + reverseFunction.reverse(userInput));

        // Close the scanner
        scanner.close();
    }
}

Output:

Reversed word using lambda function: tniopTavaj
Enter a string to be reversed:
A Java Website
After reversing: etisbeW avaJ A

Example 2

Filename: StringLambdaExample2.java

import java.util.*;
import java.util.stream.*;

public class StringLambdaExample2 {
    public static void main(String[] args) {
        // Input string
        String inputString = " javaTpoint";
        // Create an iterator for characters in reverse order
        Iterator<Character> charIterator = inputString.chars()
                .mapToObj(item -> (char) item)
                .collect(Collectors.toCollection(ArrayDeque::new))
                .descendingIterator();

        // Convert the iterator to a reversed string using Stream API
        String reversedString = StreamSupport
                .stream(Spliterators.spliteratorUnknownSize(charIterator, Spliterator.ORDERED), false)
                .map(Object::toString)
                .collect(Collectors.joining(""));

        // Print the reversed string
        System.out.println(reversedString);
    }
}

Output: