Reverse order of characters in every entry in an ArrayList

Question

I have an ArrayList with a number of entries, and I want to reverse the order or the characters, so if my code looks like this:

public class Test {

ArrayList<String> aa = new ArrayList<String>();

aa.add("hello");
aa.add("goodbye");

(reverse them in some way)


}

Then what I want the ArrayList to contain is:

olleh
eybdoog

I've only managed to change the order of the entries in the entire ArrayList with Collections.reverse, but that really doesn't do what I want to.

It's actually not the same thing. The OP wants to keep the order of the arraylist elements, but wants to replace each element with that element reversed as a string. — Chris Gerken, Apr 24 '13 at 18:05

score 3 · Answer 1 · answered Apr 24 '13 at 18:07

The StringBuilder class (mutable strings) contains a reverse operation that switches the characters of the StringBuilder.

int size = aa.size();
for(int i = 0; i < size; ++i)
{
    StringBuilder builder = new StringBuilder(aa.get(i));
    builder.reverse();    //reverse the StringBuilder
    aa.set(i, builder.toString());
}

score 1 · Accepted Answer · answered Apr 24 '13 at 18:10

1

Quick and dirty version - changing the Strings inside the original ArrayList:

for(int i = 0; i < aa.size(); i++) {
    aa.set(i, new StringBuilder(aa.get(i)).reverse().toString());
}

answered Apr 24 '13 at 18:10

Darwind

7,284
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score 0 · Answer 3 · answered Apr 24 '13 at 18:12

This is a linear time implementation, modifying the list in place.

public void reverseStr(List<String> theArgs) {
   for(int i = 0; i < theArgs.size(); i++) {
       String s = theArgs.get(i);
       theArgs.set(i, new StringBuffer(s).reverse().toString());
   }
}

score -2 · Answer 4 · edited May 23 '17 at 11:51

-2

do it like this:

Best way to reverse a string

    static void Main(string[] args)
    {
        var aa = new List<String>();

        aa.Add("hello");
        aa.Add("goodbye");

        var x = from s in aa select Reverse(s);

        foreach (var c in x)
            Console.WriteLine(c.ToString( ));

        Console.ReadLine();
    }

    public static string Reverse(string s)
    {
        char[] charArray = s.ToCharArray();
        Array.Reverse(charArray);
        return new string(charArray);
    }

edited May 23 '17 at 11:51

Community

1
1

answered Apr 24 '13 at 18:08

Timmerz

6,090
5
36
49

2

Is this C#? I guess the question has been tagged under Java. – Arjun Rao Apr 24 '13 at 18:17

Reverse order of characters in every entry in an ArrayList

4 Answers4