Question

I have got a char array (size 12) that can look like this:

{'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l'}  

And I would like to create (in the most efficient way) a String that would be the result of taking the characters from the array and ordering them ~randomly (let’s use that word), for example:

“ahbejclfkdig”

I tried solutions with StringBuffer and random placing, but there was the problem of positions repeating. Also, I tried Collections.shuffle, but I don’t quite get this one working. I also looked at linear feedback shift register, but I don’t think is appropriate here. It is quite simple case, I will not be operating on large numbers, so memory allocation and speed should not raise any major issues.

Answer 1

You can use shuffle but change it for StringBuilder. I would wouldn’t use StringBuffer unless you have to use old versions of Java.

public static void main(String... args) {
    StringBuilder sb = new StringBuilder("abcdefghijkl");
    for (int i = 0; i < 5; i++) {
        shuffle(sb);
        System.out.println(sb);
    }
}


public static void shuffle(StringBuilder sb) {
    Random rand = new Random();
    for (int i = sb.length() - 1; i > 1; i--) {
        int swapWith = rand.nextInt(i);
        char tmp = sb.charAt(swapWith);
        sb.setCharAt(swapWith, sb.charAt(i));
        sb.setCharAt(i, tmp);
    }
}

prints

kbljdhieagcf
gefabkhdclij
hbkfjilcgade
eacihdkjfgbl
hbjcfegdilka