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. — user6073886
– user6073886, Commented Feb 21, 2017 at 17:52
Possible duplicate of Retrieving a random item from ArrayList — moondaisy
– moondaisy, Commented Feb 21, 2017 at 17:52
@moondaisy That's a bad one to link in my opinion because the actual answer is hidden in a comment to the accepted answer. — KarelPeeters
– KarelPeeters, Commented Feb 21, 2017 at 17:53

Dreando · Accepted Answer · 2017-02-21 18:04:25Z

1

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);
}

answered Feb 21, 2017 at 18:04

Dreando

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Comments

Lavaman65 · Accepted Answer · 2017-02-21 18:08:35Z

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, 2017 at 18:08

Lavaman65

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