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Liang Chapter 27 Modified HASHing Source Code
package chapter27;
import java.util.LinkedList;
public class MyHashMap<K, V> implements MyMap<K, V> {
// Define the default hash table size. Must be a power of 2
private static int DEFAULT_INITIAL_CAPACITY = 4;
// Define the maximum hash table size. 1 << 30 is same as 2^30
private static int MAXIMUM_CAPACITY = 1 << 30;
// Current hash table capacity. Capacity is a power of 2
private int capacity;
// Define default load factor
private static double DEFAULT_MAX_LOAD_FACTOR = 0.75;
// Specify a load factor used in the hash table
private double loadFactorThreshold;
// The number of entries in the map
private int size = 0;
// Hash table is an array with each cell that is a linked list
LinkedList<MyMap.Entry<K, V>>[] table;
/** Construct a map with the default capacity and load factor */
public MyHashMap() {
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_MAX_LOAD_FACTOR);
}
/**
* Construct a map with the specified initial capacity and default load factor
*/
public MyHashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_MAX_LOAD_FACTOR);
}
/**
* Construct a map with the specified initial capacity and load factor
*/
public MyHashMap(int initialCapacity, double loadFactorThreshold) {
if (initialCapacity > MAXIMUM_CAPACITY)
this.capacity = MAXIMUM_CAPACITY;
else
this.capacity = trimToPowerOf2(initialCapacity);
this.loadFactorThreshold = loadFactorThreshold;
table = new LinkedList[capacity];
}
@Override /** Remove all of the entries from this map */
public void clear() {
size = 0;
removeEntries();
}
@Override /** Return true if the specified key is in the map */
public boolean containsKey(K key) {
if (get(key) != null)
return true;
else
return false;
}
@Override /** Return true if this map contains the value */
public boolean containsValue(V value) {
for (int i = 0; i < capacity; i++) {
if (table[i] != null) {
LinkedList<Entry<K, V>> bucket = table[i];
for (Entry<K, V> entry : bucket)
if (entry.getValue().equals(value))
return true;
}
}
return false;
}
@Override /** Return a set of entries in the map */
public java.util.Set<MyMap.Entry<K, V>> entrySet() {
java.util.Set<MyMap.Entry<K, V>> set = new java.util.HashSet<>();
for (int i = 0; i < capacity; i++) {
if (table[i] != null) {
LinkedList<Entry<K, V>> bucket = table[i];
for (Entry<K, V> entry : bucket)
set.add(entry);
}
}
return set;
}
@Override /** Return the value that matches the specified key */
public V get(K key) {
int bucketIndex = hash(key.hashCode());
if (table[bucketIndex] != null) {
LinkedList<Entry<K, V>> bucket = table[bucketIndex];
for (Entry<K, V> entry : bucket)
if (entry.getKey().equals(key))
return entry.getValue();
}
return null;
}
@Override /** Return true if this map contains no entries */
public boolean isEmpty() {
return size == 0;
}
@Override /** Return a set consisting of the keys in this map */
public java.util.Set<K> keySet() {
java.util.Set<K> set = new java.util.HashSet<K>();
for (int i = 0; i < capacity; i++) {
if (table[i] != null) {
LinkedList<Entry<K, V>> bucket = table[i];
for (Entry<K, V> entry : bucket)
set.add(entry.getKey());
}
}
return set;
}
@Override /** Add an entry (key, value) into the map */
public V put(K key, V value) {
if (get(key) != null) { // The key is already in the map
int bucketIndex = hash(key.hashCode());
LinkedList<Entry<K, V>> bucket = table[bucketIndex];
for (Entry<K, V> entry : bucket)
if (entry.getKey().equals(key)) {
V oldValue = entry.getValue();
// Replace old value with new value
entry.value = value;
// Return the old value for the key
return oldValue;
}
}
// Check load factor
if (size >= capacity * loadFactorThreshold) {
if (capacity == MAXIMUM_CAPACITY)
throw new RuntimeException("Exceeding maximum capacity");
rehash();
}
int bucketIndex = hash(key.hashCode());
// Create a linked list for the bucket if it is not created
if (table[bucketIndex] == null) {
table[bucketIndex] = new LinkedList<Entry<K, V>>();
}
// Add a new entry (key, value) to hashTable[index]
table[bucketIndex].add(new MyMap.Entry<K, V>(key, value));
size++; // Increase size
return value;
}
@Override /** Remove the entries for the specified key */
public void remove(K key) {
int bucketIndex = hash(key.hashCode());
// Remove the first entry that matches the key from a bucket
if (table[bucketIndex] != null) {
LinkedList<Entry<K, V>> bucket = table[bucketIndex];
for (Entry<K, V> entry : bucket)
if (entry.getKey().equals(key)) {
bucket.remove(entry);
size--; // Decrease size
break; // Remove just one entry that matches the key
}
}
}
@Override /** Return the number of entries in this map */
public int size() {
return size;
}
@Override /** Return a set consisting of the values in this map */
public java.util.Set<V> values() {
java.util.Set<V> set = new java.util.HashSet<>();
for (int i = 0; i < capacity; i++) {
if (table[i] != null) {
LinkedList<Entry<K, V>> bucket = table[i];
for (Entry<K, V> entry : bucket)
set.add(entry.getValue());
}
}
return set;
}
/** Hash function */
private int hash(int hashCode) {
return supplementalHash(hashCode) & (capacity - 1);
}
/** Ensure the hashing is evenly distributed */
private static int supplementalHash(int h) {
h ^= (h >>> 20) ^ (h >>> 12);
return h ^ (h >>> 7) ^ (h >>> 4);
}
/** Return a power of 2 for initialCapacity */
private int trimToPowerOf2(int initialCapacity) {
int capacity = 1;
while (capacity < initialCapacity) {
capacity <<= 1;
}
return capacity;
}
/** Remove all entries from each bucket */
private void removeEntries() {
for (int i = 0; i < capacity; i++) {
if (table[i] != null) {
table[i].clear();
}
}
}
/** Rehash the map */
private void rehash() {
java.util.Set<Entry<K, V>> set = entrySet(); // Get entries
capacity <<= 1; // Double capacity
table = new LinkedList[capacity]; // Create a new hash table
size = 0; // Reset size to 0
for (Entry<K, V> entry : set) {
put(entry.getKey(), entry.getValue()); // Store to new table
}
}
@Override
public String toString() {
StringBuilder builder = new StringBuilder("[");
for (int i = 0; i < capacity; i++) {
if (table[i] != null && table[i].size() > 0)
for (Entry<K, V> entry : table[i])
builder.append(entry);
}
builder.append("]");
return builder.toString();
}
}
package chapter27;
import java.util.*;
@SuppressWarnings("unchecked")
public class MyHashSet<E> implements Collection<E> {
// Define the default hash table size. Must be a power of 2
private static int DEFAULT_INITIAL_CAPACITY = 4;
// Define the maximum hash table size. 1 << 30 is same as 2^30
private static int MAXIMUM_CAPACITY = 1 << 30;
// Current hash table capacity. Capacity is a power of 2
private int capacity;
// Define default load factor
private static double DEFAULT_MAX_LOAD_FACTOR = 0.75;
// Specify a load factor threshold used in the hash table
private double loadFactorThreshold;
// The number of elements in the set
private int size = 0;
// Hash table is an array with each cell that is a linked list
private LinkedList<E>[] table;
/** Construct a set with the default capacity and load factor */
public MyHashSet() {
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_MAX_LOAD_FACTOR);
}
/**
* Construct a set with the specified initial capacity and default load factor
*/
public MyHashSet(int initialCapacity) {
this(initialCapacity, DEFAULT_MAX_LOAD_FACTOR);
}
/**
* Construct a set with the specified initial capacity and load factor
*/
public MyHashSet(int initialCapacity, double loadFactorThreshold) {
if (initialCapacity > MAXIMUM_CAPACITY)
this.capacity = MAXIMUM_CAPACITY;
else
this.capacity = trimToPowerOf2(initialCapacity);
this.loadFactorThreshold = loadFactorThreshold;
table = new LinkedList[capacity];
}
@Override /** Remove all elements from this set */
public void clear() {
size = 0;
removeElements();
}
@Override /** Return true if the element is in the set */
public boolean contains(Object e) {
int bucketIndex = hash(e.hashCode());
if (table[bucketIndex] != null) {
LinkedList<E> bucket = table[bucketIndex];
return bucket.contains(e);
}
return false;
}
@Override /** Add an element to the set */
public boolean add(E e) {
if (contains(e)) // Duplicate element not stored
return false;
if (size + 1 > capacity * loadFactorThreshold) {
if (capacity == MAXIMUM_CAPACITY)
throw new RuntimeException("Exceeding maximum capacity");
rehash();
}
int bucketIndex = hash(e.hashCode());
// Create a linked list for the bucket if it is not created
if (table[bucketIndex] == null) {
table[bucketIndex] = new LinkedList<E>();
}
// Add e to hashTable[index]
table[bucketIndex].add(e);
size++; // Increase size
return true;
}
@Override /** Remove the element from the set */
public boolean remove(Object e) {
if (!contains(e))
return false;
int bucketIndex = hash(e.hashCode());
// Create a linked list for the bucket if it is not created
if (table[bucketIndex] != null) {
LinkedList<E> bucket = table[bucketIndex];
bucket.remove(e);
}
size--; // Decrease size
return true;
}
@Override /** Return true if the set contains no elements */
public boolean isEmpty() {
return size == 0;
}
@Override /** Return the number of elements in the set */
public int size() {
return size;
}
@Override /** Return an iterator for the elements in this set */
public java.util.Iterator<E> iterator() {
return new MyHashSetIterator(this);
}
/** Inner class for iterator */
private class MyHashSetIterator implements Iterator<E> {
// Store the elements in a list
private ArrayList<E> list;
private int current = 0; // Point to the current element in list
/** Create a list from the set */
public MyHashSetIterator(MyHashSet<E> set) {
list = setToList();
}
@Override /** Next element for traversing? */
public boolean hasNext() {
return current < list.size();
}
@Override /** Get current element and move cursor to the next */
public E next() {
return list.get(current++);
}
@Override /** Remove the element returned by the last next() */
public void remove() {
}
}
/** Hash function */
private int hash(int hashCode) {
return hashCode & (capacity - 1);
}
/** Return a power of 2 for initialCapacity */
private int trimToPowerOf2(int initialCapacity) {
int capacity = 1;
while (capacity < initialCapacity) {
capacity <<= 1;
}
return capacity;
}
/** Remove all e from each bucket */
private void removeElements() {
for (int i = 0; i < capacity; i++) {
if (table[i] != null) {
table[i].clear();
}
}
}
/** Rehash the set */
private void rehash() {
ArrayList<E> list = setToList(); // Copy to a list
capacity <<= 1; // Double capacity
table = new LinkedList[capacity]; // Create a new hash table
size = 0; // Reset size
for (E element : list) {
add(element); // Add from the old table to the new table
}
}
/** Copy elements in the hash set to an array list */
private ArrayList<E> setToList() {
ArrayList<E> list = new ArrayList<>();
for (int i = 0; i < capacity; i++) {
if (table[i] != null) {
for (E e : table[i]) {
list.add(e);
}
}
}
return list;
}
@Override
public String toString() {
ArrayList<E> list = setToList();
StringBuilder builder = new StringBuilder("[");
// Add the elements except the last one to the string builder
for (int i = 0; i < list.size() - 1; i++) {
builder.append(list.get(i) + ", ");
}
// Add the last element in the list to the string builder
if (list.size() == 0)
builder.append("]");
else
builder.append(list.get(list.size() - 1) + "]");
return builder.toString();
}
@Override
public boolean addAll(Collection<? extends E> arg0) {
// Left as an exercise
return false;
}
@Override
public boolean containsAll(Collection<?> arg0) {
// Left as an exercise
return false;
}
@Override
public boolean removeAll(Collection<?> arg0) {
// Left as an exercise
return false;
}
@Override
public boolean retainAll(Collection<?> arg0) {
// Left as an exercise
return false;
}
@Override
public Object[] toArray() {
// Left as an exercise
return null;
}
@Override
public <T> T[] toArray(T[] arg0) {
// Left as an exercise
return null;
}
}
package chapter27;
public interface MyMap<K, V> {
/** Remove all of the entries from this map */
public void clear();
/** Return true if the specified key is in the map */
public boolean containsKey(K key);
/** Return true if this map contains the specified value */
public boolean containsValue(V value);
/** Return a set of entries in the map */
public java.util.Set<Entry<K, V>> entrySet();
/** Return the first value that matches the specified key */
public V get(K key);
/** Return true if this map contains no entries */
public boolean isEmpty();
/** Return a set consisting of the keys in this map */
public java.util.Set<K> keySet();
/** Add an entry (key, value) into the map */
public V put(K key, V value);
/** Remove the entries for the specified key */
public void remove(K key);
/** Return the number of mappings in this map */
public int size();
/** Return a set consisting of the values in this map */
public java.util.Set<V> values();
/** Define inner class for Entry */
public static class Entry<K, V> {
K key;
V value;
public Entry(K key, V value) {
this.key = key;
this.value = value;
}
public K getKey() {
return key;
}
public V getValue() {
return value;
}
@Override
public String toString() {
return "[" + key + ", " + value + "]";
}
}
}
package chapter27;
public class TestMyHashMap {
public static void main(String[] args) {
// Create a map
MyMap<String, Integer> map = new MyHashMap<>();
map.put("Smith", 30);
map.put("Anderson", 31);
map.put("Lewis", 29);
map.put("Cook", 29);
map.put("Smith", 65);
System.out.println("Entries in map: " + map);
System.out.println("The age for " + "Lewis is " +
map.get("Lewis"));
System.out.println("Is Smith in the map? " +
map.containsKey("Smith"));
System.out.println("Is age 33 in the map? " +
map.containsValue(33));
map.remove("Smith");
System.out.println("Entries in map: " + map);
map.clear();
System.out.println("Entries in map: " + map);
}
}
package chapter27;
public class TestMyHashSet {
public static void main(String[] args) {
// Create a MyHashSet
java.util.Collection<String> set = new MyHashSet<>();
set.add("Smith");
set.add("Anderson");
set.add("Lewis");
set.add("Cook");
set.add("Smith");
System.out.println("Elements in set: " + set);
System.out.println("Number of elements in set: " + set.size());
System.out.println("Is Smith in set? " + set.contains("Smith"));
set.remove("Smith");
System.out.print("Names in set in uppercase are ");
for (String s: set)
System.out.print(s.toUpperCase() + " ");
set.clear();
System.out.println("\nElements in set: " + set);
}
}
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