How to shuffle characters in a string without using Collections.shuffle(...)?

What an annoying problem. I finally ended up with this:

import java.util.Collections;
import com.google.common.primitives.Chars;
import org.apache.commons.lang3.StringUtils;

String shuffle(String s) {
    List<Character> chars = Chars.asList(s.toCharArray());
    Collections.shuffle(chars);
    return StringUtils.join(chars.stream().toArray());
}

Yes, two libraries :)

How about this:

public static String shuffle(String text) {
    char[] characters = text.toCharArray();
    for (int i = 0; i < characters.length; i++) {
        int randomIndex = (int)(Math.random() * characters.length);
        char temp = characters[i];
        characters[i] = characters[randomIndex];
        characters[randomIndex] = temp;
    }
    return new String(characters);
}

I dont know anything simpler. But you can use the Math.rand() functionality to generate a random number within the range of the character's length without replace and that would give you a shuffled output

public class Shuffle {
    public static void main(String[] args) {
        Shuffle s = new Shuffle();
        s.shuffle("hello");

    }
    public void shuffle(String input){
        List<Character> characters = new ArrayList<Character>();
        for(char c:input.toCharArray()){
            characters.add(c);
        }
        StringBuilder output = new StringBuilder(input.length());
        while(characters.size()!=0){
            int randPicker = (int)(Math.random()*characters.size());
            output.append(characters.remove(randPicker));
        }
        System.out.println(output.toString());
    }
}
/*
Sample outputs
hlleo
llheo
leohl
lleho
*/

Not great performance, but quite readable in my opinion:

public static String shuffleString(String string)
{
  List<String> letters = Arrays.asList(string.split(""));
  Collections.shuffle(letters);
  String shuffled = "";
  for (String letter : letters) {
    shuffled += letter;
  }
  return shuffled;
}