Rearrange a number to get the largest number - JAVA

I have generated a random 4 digit number, I now need to take the number and re-arrange it to create the largest possible - for example if i generated 3982 I then want to rearrange it to create 9832 (in a new variable) I also need to rearrange it to become the smallest (2389) in another new variable.. how do i do this?

So far I have...

public static void main(String[] args) {
    Random randomGenerator = new Random();
    int randomInteger = randomGenerator.nextInt(9999);
    System.out.println(String.format("%04d", randomInteger));