How to select the highest number in arraylist in an inheritance class [duplicate]

This question already has an answer here:

• how to get maximum value from the List/ArrayList 9 answers

I would like the computer to generate the largest number, how do I amend list below!. Please help?

 public int getRandomNumber(ArrayList<Integer> list) {
       Random rn = new Random();
       int i = rn.nextInt(list.size());
       return list.get(i);
}

Many thanks