Retrieve random object from ArrayList

Question

The method below is the method I am using to populate my array. However I wish to return a random deals_informationobject from my ArrayList of type Deals_Information but am not quite sure how.

    public void populateArray() {

    databaseReference.child("FruitDeals").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            Iterable<DataSnapshot> children = dataSnapshot.getChildren();
            final ArrayList<Deals_Information> myArray = new ArrayList<>();

            for (DataSnapshot child : children) {
                Deals_Information deals_information = child.getValue(Deals_Information.class);
                myArray.add(deals_information);
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

java.lang.Random is your friend....as one could have probably found out by typing java + random into google. — OH GOD SPIDERS, Feb 21 '17 at 17:52
Possible duplicate of [Retrieving a random item from ArrayList](http://stackoverflow.com/questions/5034370/retrieving-a-random-item-from-arraylist) — moondaisy, Feb 21 '17 at 17:52
Possible duplicate of [Randomly select an item from a list](http://stackoverflow.com/questions/12487592/randomly-select-an-item-from-a-list) — Todd Sewell, Feb 21 '17 at 17:53
@moondaisy That's a bad one to link in my opinion because the actual answer is hidden in a comment to the accepted answer. — Todd Sewell, Feb 21 '17 at 17:53

score 1 · Answer 1 · answered Feb 21 '17 at 18:04

Use Random to get a random int from the range of 0 and the size-1 of your collection.

Since Java 1.7, the recommended Random implementation is ThreadLocalRandom.

private int randomInt(final int from, final int to) {
    return ThreadLocalRandom.current().nextInt(from, to);
}

score 0 · Answer 2 · answered Feb 21 '17 at 18:08

0

Because ArrayLists have a get() function, the way to do this is to first generate a random number by using the math.random() function, and then use the get() function of your ArrayList to call the object at that randomly generated index.

answered Feb 21 '17 at 18:08

Lavaman65

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Retrieve random object from ArrayList

2 Answers2