Java: Retrieve a random discontinuous Sublist of an ArrayList (most efficient way)

Question

put simply my question is: What is the most efficient way to retrieve a random discontinuous sublist of an ArrayList with a given size.

The following is my own design, which works but seems a little clunky to me. It is my first JAVA program by the way so please excuse if my code or question is not according to best practice ;)

Remarks:
- my list does not contain duplicates
- I guessed that it might be faster to remove items instead of adding them if the AimSize is more than half of the size of the original list

public ArrayList<Vokabel> subList(int AimSize) {
    ArrayList<Vokabel> tempL = new ArrayList<Vokabel>();
    Random r = new Random();
    LinkedHashSet<Vokabel> tempS = new LinkedHashSet<Vokabel>();

    tempL = originalList;

    // If the size is to big just leave the list and change size 
    // (in the real code there is no pass-by-value problem ;)
    if (!(tempL.size() > AimSize)) {
        AimSize = tempL.size();
    // set to avoid duplicates and get a random order
    } else if (2* AimSize < tempL.size()) {
        while (tempS.size() < AimSize) {
            tempS.add(tempL.get(r.nextInt(tempL.size())));
        }
        tempL = new ArrayList<Vokabel>(tempS);
    // little optimization if it involves less loops
    // to delete entries to get to the right size, than to add them
    // the List->Set->List conversion at the end is there to reorder the items
    } else {
        while (tempL.size() > AimSize) {
            tempL.remove(r.nextInt(tempL.size()));
        }
        tempL = new ArrayList<Vokabel>(new LinkedHashSet<Vokabel>(tempL));

    }

    return tempL;
}

Answer 1

Warning: This is coded in my browser. It may not even compile!

Using Collections.shuffle and List.subList will do the job.

public static <T> List<T> randomSubList(List<T> list, int newSize) {
    list = new ArrayList<>(list);
    Collections.shuffle(list);
    return list.subList(0, newSize);
}