Reverse a string for only the alphabets in a sentence not numbers or special characters in java

Question

I want to implement a method to return a string after reversing only the alphabets [a-zA-Z] in a sentence, not number or special characters. Reversing has to be done word-by-word. eg: for 25000rs for 1 LCD it should be 25000sr rof 1 DCL .

public class Main {
    static String reverseWords(String inputString) { 
    String[] words = inputString.split(" ");

    String reverseString = "";

    for (int i = 0; i < words.length; i++) 
    {
        String word = words[i];

        String reverseWord = "";

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

        reverseString = reverseString + reverseWord + " ";
    }
    return reverseString;
}
public static void main(String[] args)
{
    String str1 = "1 cup of hot coffee costs 8.00, whereas cold coffee costs 45.00."; 
    System.out.println(reverseWords(str1));  

    String str2 = "It Costs 25000rs for 1 LCD Projector."; 
    System.out.println(reverseWords(str2)); 

    String str3 = "8990.33"; 
    System.out.println(reverseWords(str3)); 
}
}  

This is the output I want:

1 puc fo toh eeffoc stsoc 8.00, saerehw dloc eeffoc stsoc 45.00.

tI stsoC 25000sr rof 1 DCL rotcejorP.

8990.33

This is the output I am getting:

1 puc fo toh eeffoc stsoc,00.8 saerehw dloc eeffoc stsoc.00.54

tI stsoC sr00052 rof 1 DCL.rotcejorP

33.0998

Answer 1

You are just splitting at space characters, which makes every sequence of non-space characters a “word”.

This task is a canonical use case for the regex Matcher 's appendReplacement / appendTail loop, which you can always use when the intended replacement logic is too complex for a simple replaceAll(String regex, String replacement) on a String :

static final Pattern WORD = Pattern.compile("\\pL+"); // class "L" means "letter"

static String reverseWords(String inputString) { 
    Matcher m = WORD.matcher(inputString);
    if(!m.find()) return inputString;
    StringBuffer sb = new StringBuffer(inputString.length());
    do {
        m.appendReplacement(sb, new StringBuilder(m.group()).reverse().toString());
    } while(m.find());
    return m.appendTail(sb).toString();
}

(Starting with Java 9, this API also supports using StringBuilder instead of StringBuffer .

---

But in this specific case, the operation can also be done slightly more efficient:

static String reverseWords(String inputString) { 
    Matcher m = WORD.matcher(inputString);
    if(!m.find()) return inputString;
    StringBuilder sb = new StringBuilder(inputString);
    do {
        for(int ix1 = m.start(), ix2 = m.end() - 1; ix1 < ix2; ix1++, ix2--) {
            sb.setCharAt(ix1, inputString.charAt(ix2));
            sb.setCharAt(ix2, inputString.charAt(ix1));
        }
    } while(m.find());
    return sb.toString();
}

Answer 2

import java.util.*; 

public class Main {
    static String reverse(String inputString) { 
    String[] words = inputString.split(" ");
    boolean set = false; 
    String reverseString = "";

    for (int i = 0; i < words.length; i++) 
    {
        String word = words[i];

        String reverseWord = "";

        for (int j = word.length()-1; j >= 0; j--) 
        {  
            if (Character.isAlphabetic(word.charAt(j))){
                
            reverseWord = reverseWord + word.charAt(j);
            set = false; 
        }else{
            set = true ; 
            break ; 
        }
        }
        if(set == true){
            reverseString = reverseString + reverseWord + word +  " "; 
        }
        
        reverseString = reverseString + reverseWord +  " ";
      
    }
    return reverseString;
}

public static void main(String[] args)
{
    String st1 = "1 cup of hot coffee costs 8.00, whereas cold coffee costs 45.00.";
    System.out.println(Main.reverse(st1));  

    String st2 = "It Costs 25000rs for 1 LCD Projector."; 
    System.out.println(Main.reverse(st2)); 

    String st3 = "8990.33"; 
    System.out.println(Main.reverse(st3)); 
    
    String st4 = "Hello Everyone Today we are going to learn 1-10 table."; 
    System.out.println(Main.reverse(st4)); 
}
}