CustomHashMapImpl.java

package maps.customhashmap;

/**
 * Implementing hashmap.
 * User: rpanjrath
 * Date: 9/22/13
 * Time: 1:17 PM
 */
public class CustomHashMapImpl<K, V> implements CustomHashMap<K, V> {

 private int DEFAULT_BUCKET_COUNT = 10;
 Entry[] entryBuckets;

 public CustomHashMapImpl() {
 this.entryBuckets = new Entry[DEFAULT_BUCKET_COUNT];
 }

 public CustomHashMapImpl(int size) {
 this.entryBuckets = new Entry[size];
 }

 @Override
 public void put(K key, V value) {
 Entry<K, V> newEntry = new Entry<K, V>(key, value);
 if (key == null) {
 throw new IllegalArgumentException("Key " + key + " cannot be null.");
 }
 int bucketIndex = findBucketUsingHashFunction(key.hashCode());
 // Nothing in the bucket. Its a first entry at that bucket[hashcode(key)]
 if (entryBuckets[bucketIndex] == null) {
 entryBuckets[bucketIndex] = newEntry;
 } else {
 Entry<K, V> entry = entryBuckets[bucketIndex];
 // If same key but different value, then update the value.
 if (entry.getKey().equals(key)) {
 entry.setValue(value);
 } else {
 // Different key but same hashcode.. collision.. add to linkedlist
 while (entry.getNext() != null) {
 entry = entry.getNext();
 }
 entry.setNext(newEntry);
 }
 }
 }

 @Override
 public V get(K key) {
 if (key == null) {
 throw new IllegalArgumentException("Key " + key + " cannot be null.");
 }
 int bucketIndex = findBucketUsingHashFunction(key.hashCode());
 Entry<K, V> entry = entryBuckets[bucketIndex];
 // Loop through bucket if multiple entries.
 // current entry will be found once the inputKey is equal to entryKey
 // Collisions: Two different keys have same hashCode. It results that both Entries with respective keys
 // are added into same bucket.
 while (entry != null && !key.equals(entry.getKey())) {
 entry = entry.getNext();
 }
 return entry != null ? entry.getValue() : null;
 }

 // This is the hashFunction which will decide on the bucket.
 private int findBucketUsingHashFunction(int hashCode) {
 return hashCode % entryBuckets.length;
 }

 @Override
 public boolean remove(K key) {
 return false;
 }

 private static class Entry<K, V> {

 private Entry<K, V> next;
 private final K key;
 private V value;

 public Entry(K key, V value) {
 this.key = key;
 this.value = value;
 }

 private V getValue() {
 return value;
 }

 private void setValue(V value) {
 this.value = value;
 }

 private K getKey() {
 return key;
 }

 private Entry<K, V> getNext() {
 return next;
 }

 private void setNext(Entry<K, V> next) {
 this.next = next;
 }
 }
}