I am trying to reverse an array the user inputs like {hello, Donald, Trump} -> pmurT, dlanoD etc but it outputs [null]

Question

I'm new to java and wanted to reverse an array the user inputs (including character) so apple, banana becomes ananab, elppa. But it outputs [null]

package test;

import java.util.Arrays;
import java.util.Collections;

import javax.swing.JOptionPane;

public class WhileWarmup{

    public static void main(String[] args) {
        String shoppinglist = JOptionPane.showInputDialog("What do you want to manipulate");
        String[]Shoppinglist = shoppinglist.split(",");
        String[]Shoppinglist1 = shoppinglist.split(",");
        
        int num = Shoppinglist.length;
        String bruh = "";
        String bruh1 = "";
        while (num >= 0) {
            Shoppinglist1 = Arrays.copyOfRange(Shoppinglist,num,num + 1);
            Collections.reverse(Arrays.asList(Shoppinglist1));
            bruh1 =  Arrays.toString(Shoppinglist1);
            bruh = bruh + bruh1;
            num = num - 1;
            System.out.println(bruh);
        }
    }
}

Did you try debugging your code? It seems to me that `Arrays.copyOfRange` doesn't do what you think it does. — Amongalen, Aug 19 '20 at 11:11
Does this answer your question? [Reverse a string in Java](https://stackoverflow.com/questions/7569335/reverse-a-string-in-java) — Amongalen, Aug 19 '20 at 11:12
Also note: you are very much overcomplicating your own life. The problem you want to understand: how to fully reverse some array of strings. Then write code that just does that: trying to reverse a known HARDCODED array of strings. You see, all that Swing UI stuff, and the time spent for TYPING in your values ... that does not relate to your underlying problem AT ALL. Remember: reduce your problem to its core, and get rid of anything that does not contribute to it. Then you wouldnt need to give your examples in the question title. Then your code would tell us what you did. — GhostCat, Aug 19 '20 at 11:28
And: learn about java naming conventions. variable names go camelCase, always. So "Shopplinglist" rather sounds like the name of some class. And of course. the real answer is: dont just blindly use some library method. Read the corresponding java doc to understand what it is supposed to do — GhostCat, Aug 19 '20 at 11:29
Finally: what did you expect? The person whose name I shall not say that you are using in your example ... basically resembles an empty void. It isnt surprising that reversing that results in null. — GhostCat, Aug 19 '20 at 11:30
Please [edit] your question. It is **entirely** unclear what you want to achieve. Do you want to reverse each `String` in an array or only the array itself but leave the items alone?? — Lino, Aug 19 '20 at 11:54
Downvoted: we asked you repeatedly to improve your question to make it answerable. You expect other people to spend their free time to help you with your problem. So you please spend the time needed to improve your content. — GhostCat, Aug 19 '20 at 13:39
What I understand from your ques is you want to reverse the array with reversing each array element. {hello,"trump"} will be {"pmurt","olleh"} - Doesn't it reverse the string of the array? Not understanding why every answer is downvoted when people have answered correctly. — garima garg, Aug 19 '20 at 13:39

George Z. · Answer 1 · 2020-08-19T11:28:11.307

When it comes to reversing a String, StringBuilder#reverse is always there:

    public static void main(String[] args) {
        List<String> wordList = Arrays.asList("hello", "Donald", "Trump");
        System.out.println(reverseListAndItsElements(wordList));
    }

    public static List<String> reverseListAndItsElements(List<String> list) {
        List<String> reversed = new ArrayList<>(list);//Create a copy
        Collections.reverse(reversed);
        return reversed.stream().map(s -> new StringBuilder(s).reverse().toString())
            .collect(Collectors.toList());
    }

Prints:

[pmurT, dlanoD, olleh]

And in case you do not want to mess with lists:

public static void main(String[] args) {
    String original = "hello,Donald,Trump";
    String[] split = original.split(",");
    String[] reversedSplit = new String[split.length];
    IntStream.range(0, split.length).forEach(index -> {
        reversedSplit[index] = new StringBuilder(split[index]).reverse().toString();
    });
    System.out.println(Arrays.toString(reversedSplit));
}

@WilliamGreenfield I updated my answer. By the way, your title says you want to reverse the strings. — George Z., Aug 19 '20 at 11:28

score 0 · Answer 2 · 2020-08-19T12:39:28.217

0

Try this.

String[] input = {"hello", "Donald", "Trump"};
String[] reversed = new StringBuilder(String.join(",", input))
    .reverse().toString().split(",");
System.out.println(Arrays.toString(reversed));

output:

[pmurT, dlanoD, olleh]

edited Aug 19 '20 at 12:39

answered Aug 19 '20 at 12:32

Junaid Subhani · Answer 3 · 2020-08-19T11:30:44.663

-1

you can use the following code

public static List<String> reverseList(List<String> list) {
        List<String> reversed = new ArrayList<>(list);
        Collections.reverse(reversed);
        return reversed.stream().collect(Collectors.toList());
    }

edited Aug 19 '20 at 11:30

answered Aug 19 '20 at 11:25

Junaid Subhani

39
1
5

i would like to rather reverse the array not the string – William Greenfield Aug 19 '20 at 11:28
3

@WilliamGreenfield The question title suggests otherwise. So: get clear on your requirements. You asked "how to do X", and well, this answer explains what you asked for. – GhostCat Aug 19 '20 at 11:31
I updated the code it will only reverse the order of elements. Hope it will help – Junaid Subhani Aug 19 '20 at 11:31

score -1 · Answer 4 · answered Aug 19 '20 at 11:38

This code can be used for String array reverse implementation. There are many ways of reversing a string. One is using StringBuilder I have used.

public class Main
{
 static String[] arr={"hello", "Donald", "Trump"};
  public static void main (String[]args)
 {
String[] strA=  reverseTheString(arr);

for(int i=0;i<strA.length;i++){
    System.out.println(""+strA[i]);
}
}

// This is actual method for reverse an array elements.

public static String[] reverseTheString(String[] arr){
 String[] reverseArray=new String[arr.length];
int j=arr.length-1;

for(int i=0;i<arr.length;i++)
  {
      StringBuilder sb=new StringBuilder(arr[i]);
    reverseArray[j]=sb.reverse().toString();
    j--;
 }
return reverseArray;
 }
}

Not sure why its downvoted. It's giving the required result and user dint write any specific algo/logic to use. — garima garg, Aug 19 '20 at 13:34

I am trying to reverse an array the user inputs like {hello, Donald, Trump} -> pmurT, dlanoD etc but it outputs [null]

4 Answers4