Resizing HashMap

Question

I created a HashMap to store entries. Now when there is a collision of hashcodes, how can I resize the buckets. Right now I just have the buckets set to an arbitrary prime number and I can't figure out how to make the buckets resize themselves if buckets reach capacity.

public class BucketList<K, V> extends LinkedList<Bucket<K, V>> {

    private final int NUM_BUCKETS = 997; //Arbitrary prime number 

    public BucketList() {
        initializeBuckets();
    }
    public void add(int index, BucketEntry<K, V> entry) {

        Bucket<K, V> bucket = get(index);

        if (bucket == null){
            set(index, new Bucket<>(entry));
        } else {
            BucketEntry<K, V> current = bucket.findEntry(entry.getKey());

            if (current != null) {
                current.setValue(entry.getValue());
            } else
            {
                bucket.add(entry);
            }
        }
    }

    private void initializeBuckets() {
        for (int i = 0; i < NUM_BUCKETS; i++) {
            add(null);
        }
    }
}