Reverse words in String Java



 Write a Java program to reverse each word in a given string.

Java program to Reverse words

import java.util.regex.Pattern;
import java.util.stream.Collectors;

public final class Strings {

    private static final Pattern PATTERN = Pattern.compile(" +");
    private static final String WHITESPACE = " ";

    private Strings() {
        throw new AssertionError("Cannot be instantiated");
    }

    public static String reverseWordsV1(String str) {

        if (str == null || str.isBlank()) {
            // or throw IllegalArgumentException
            return "";
        }

        String[] words = str.split(WHITESPACE);
        StringBuilder reversedString = new StringBuilder();

        for (String word : words) {

            StringBuilder reverseWord = new StringBuilder();

            for (int i = word.length() - 1; i >= 0; i--) {
                reverseWord.append(word.charAt(i));
            }

            reversedString.append(reverseWord).append(WHITESPACE);
        }

        return reversedString.toString();
    }

    public static String reverseWordsV2(String str) {

        // or throw IllegalArgumentException
        if (str == null || str.isBlank()) {
            return "";
        }

        return PATTERN.splitAsStream(str)
                .map(w -> new StringBuilder(w).reverse())
                .collect(Collectors.joining(WHITESPACE));
    }

    public static String reverse(String str) {

        // or throw IllegalArgumentException
        if (str == null || str.isBlank()) {
            return "";
        }

        return new StringBuilder(str).reverse().toString();
    }

}

Test

import java.util.concurrent.TimeUnit;

public class Main {

	private static final String TEXT = " Java is my fav programming language. I love Java coding";

    public static void main(String[] args) {

        System.out.println("Input text: \n" + TEXT + "\n");
        
        System.out.println("Reverse words in String via StringBuilder:");
        long startTimeV1 = System.nanoTime();
        
        String reversedV1 = Strings.reverseWordsV1(TEXT);
        
        displayExecutionTime(System.nanoTime() - startTimeV1);
        System.out.println("Reversed: \n" + reversedV1);

        System.out.println();        
        System.out.println("Reverse words in String using Java 8 functional-style:");
        long startTimeV2 = System.nanoTime();
        
        String reversedV2 = Strings.reverseWordsV2(TEXT);
        
        displayExecutionTime(System.nanoTime() - startTimeV2);
        System.out.println("Reversed: \n" + reversedV2);
        
        System.out.println();
        System.out.println("Reverse String via StringBuilder:");
        long startTimeV3 = System.nanoTime();
        
        String reversedV3 = Strings.reverse(TEXT);
        
        displayExecutionTime(System.nanoTime() - startTimeV3);
        System.out.println("Reversed: \n" + reversedV3);       
    }

    private static void displayExecutionTime(long time) {
        System.out.println("Execution time: " + time + " ns" + " ("
                + TimeUnit.MILLISECONDS.convert(time, TimeUnit.NANOSECONDS) + " ms)");
    }

}

Output:

Input text: 
 Java is my fav programming language. I love Java coding

Reverse words in String via StringBuilder:
Execution time: 49344800 ns (49 ms)
Reversed: 
 avaJ si ym vaf gnimmargorp .egaugnal I evol avaJ gnidoc 

Reverse words in String using Java 8 functional-style:
Execution time: 23643400 ns (23 ms)
Reversed: 
 avaJ si ym vaf gnimmargorp .egaugnal I evol avaJ gnidoc

Reverse String via StringBuilder:
Execution time: 31600 ns (0 ms)
Reversed: 
gnidoc avaJ evol I .egaugnal gnimmargorp vaf ym si avaJ 

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