Reverse string word by word in java (stack/ stringbuilder /example)

• Given a string in java, reverse the string word by word.
• Let us look into couple of examples to understand problem statement.
  • Example 1:
    • String inputString = “Girl Proposes Boy”
    • reverse(inputString) should be “Boy Proposes Girl”
  • Example 2:
    • String inputString = “Hell To Heaven”
    • reverse(inputString) should be “Heaven To Hell”

1. Algorithm: Reverse string word by word (java/ stack /stringbuilder)

1. Reverse String using StringBuilder
   • Split the input string using space delimiter.
   • Start appending the string from end .
   • We will get string reversed word wise.
2. Reverse String using Stack.
   • Split the input string using space delimiter.
   • Iterate through the string array (result of previous step) & push each string to stack.
   • Pop each string element from stack and concatenate the string.
   • We we get the desired output.

2. Program: Reverse string word by word (java/stack/stringbuilder /example)

package org.learn;

import java.util.Scanner;
import java.util.Stack;
import java.util.regex.Pattern;

public class ReverseWordsInString {

 public static void main(String[] args) {
  try (Scanner scanner = new Scanner(System.in)) {
   System.out.printf("1. Enter string to reverse : ");
   String inputString = scanner.nextLine();
   
   if (inputString == null || inputString.length() == 0) {
    System.out.println("Enter the valid string");
    return;
   }
   
   String reverse = reverseStringWordWise(inputString);
   System.out.printf("2. Reverse string using StringBuilder is : %s", reverse);
   
   reverse = reverseStringWordWise_Stack(inputString);
   System.out.printf("\n3. Reverse string using stack is : %s", reverse);
  }
 }

 private static String reverseStringWordWise(String inputString) {
  String[] arrString = inputString.trim().split(Pattern.quote(" "));
  StringBuilder builder = new StringBuilder();
  int length = arrString.length;

  while (--length >= 0) {
   builder.append(arrString[length]).append(" ");
  }

  return builder.toString();
 }
 
 private static String reverseStringWordWise_Stack(String inputString) {
  String[] arrString = inputString.trim().split(Pattern.quote(" "));
  Stack<String> stack = new Stack<>();
  for(String input : arrString) {
   stack.push(input);
  }
  
  StringBuilder builder = new StringBuilder();
  while( !stack.isEmpty()) {
   builder.append(stack.pop()).append(" ");
  }
  return builder.toString();
 }
}

3. Output: Reverse string word by word (java/stack/stringbuilder /example)

1. Enter string to reverse : Girl Proposes Boy
2. Reverse string using StringBuilder is : Boy Proposes Girl 
3. Reverse string using stack is : Boy Proposes Girl 

1. Enter string to reverse : Hell To Heaven
2. Reverse string using StringBuilder is : Heaven To Hell 
3. Reverse string using stack is : Heaven To Hell