If statement unexpectedly loops infinitely inside for loop-CodePudding

input: "Who lives in a pineapple under the sea?" expected output: "Who sevil in a elppaenip rednu the sea?" (reverse size 5 and above words)

I think the if statement is the problem but I don't know why it's not working. I tried using the code from the if statement block inside the main method and it works fine.

public class Testing {

    public static void main(String[] args) {
        String sentence = "Who lives in a pineapple under the sea?"; 
        System.out.println(spinWords(sentence)); 
    }
    
      public static String spinWords(String sentence) {
        String[] words = sentence.split(" "); 
        int length = words.length; 
        String spinned = ""; 
        for (int i = 0; i < length; i  ) {
            String word = words[i];  
            int wlength = word.length(); 
            if (wlength > 4) {  
                String reversed = ""; 
                for (i = wlength - 1; i >= 0; i--) {
                    reversed  = ""   word.charAt(i); 
                }
                spinned  = reversed   " ";
            } else {
              spinned  = word   " "; 
            }
        }
        spinned = spinned.trim(); 
        return spinned; 
      }
}

This is my first stack overflow question btw and I don't really know what I'm doing. I would also love to see better implementations of this code ( for learning purposes ), thanks.

CodePudding user response：

Replace the "if" block with below code. You were using the variable "i" which is used by the first "for" loop. This caused the infinite loop.

    if (wlength > 4) {  
        String reversed  = "";
         for(int j = 0; j < wlength; j  ) {
             reversed = word.charAt(j)   reversed;
         }
         spinned  = reversed   " ";
    } else {
      spinned  = word   " "; 
    }

CodePudding user response：

The issue in your code is the duplicate use of the local variable i as others have pointed out. Typically you never want a nested loop counter to use the same variable name as the outer loop counter.

There is a reason why for (int i = wlength - 1; i >= 0; i--) is a compilation error (with the int declaration added). Instead simply use another variable name:

for (int j = wlength - 1; j >= 0; j--)

This will fix the error in the code. However, since you asked for other implementations I thought I would show another option using StringBuilder, which I believe is easier to read:

public static void main(String[] args) {
    String sentence = "Who lives in a pineapple under the sea?";
    System.out.println(spinWords(sentence));
}

public static String spinWords(String sentence) {
    String[] words = sentence.split(" ");
    StringBuilder sb = new StringBuilder();

    for (String str : words) {
        if (str.length() >= 5) {
            sb.append(new StringBuilder(str).reverse());
        } else {
            sb.append(str);
        }
        sb.append(" ");
    }

    return sb.toString().trim();
}

StringBuilder is often used when concatenating a String inside of a loop, see this answer.

Additionally, StringBuilder has the reverse() method which you can use to reverse individual words instead of using a nested loop. You then just use toString to convert the StringBuilder object into a String.

Lastly, I used an enhanced for loop of for (String str : words) which allows you to loop directly on the String values instead of needing to use a loop counter.

CodePudding user response：

Here's a one-liner:

public static String spinWords(String sentence) {
    return Arrays.stream(sentence.split(" "))
      .map(word -> word.length() < 5 ? word : new StringBuilder(word).reverse().toString())
      .collect(Collectors.joining(" "));
}

See live demo.