/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package ju.util;
/**
* HashMap is an implementation of Map. All optional operations (adding and
* removing) are supported. Keys and values can be any objects.
*/
public class HashMap<K, V> extends AbstractMap<K, V> implements Map<K, V> {
/*
* Actual count of entries
*/
int elementCount;
/*
* The internal data structure to hold Entries
*/
Entry<K, V>[] elementData;
/*
* modification count, to keep track of structural modifications between the
* HashMap and the iterator
*/
int modCount = 0;
/*
* default size that an HashMap created using the default constructor would
* have.
*/
private static final int DEFAULT_SIZE = 16;
/*
* maximum ratio of (stored elements)/(storage size) which does not lead to
* rehash
*/
final float loadFactor;
/*
* maximum number of elements that can be put in this map before having to
* rehash
*/
int threshold;
static class Entry<K, V> extends MapEntry<K, V> {
final int origKeyHash;
Entry<K, V> next;
Entry(K theKey, int hash) {
super(theKey, null);
this.origKeyHash = hash;
}
Entry(K theKey, V theValue) {
super(theKey, theValue);
origKeyHash = (theKey == null ? 0 : computeHashCode(theKey));
}
}
/**
* Create a new element array
*
* @param s
* @return Reference to the element array
*/
@SuppressWarnings("unchecked")
Entry<K, V>[] newElementArray(int s) {
return new Entry[s];
}
/**
* Constructs a new empty {@code HashMap} instance.
*/
public HashMap() {
this.loadFactor = 0.75f; // default load factor of 0.75
init(DEFAULT_SIZE);
}
/**
* Constructs a new {@code HashMap} instance with the specified capacity.
*
* @param capacity
* the initial capacity of this hash map.
* @throws IllegalArgumentException
* when the capacity is less than zero.
*/
public HashMap(int capacity) {
this.loadFactor = 0.75f; // default load factor of 0.75
init(capacity);
}
/**
* Calculates the capacity of storage required for storing given number of
* elements
*
* @param x
* number of elements
* @return storage size
*/
private static final int calculateCapacity(int x) {
if(x >= 1 << 30){
return 1 << 30;
}
if(x == 0){
return 16;
}
x = x -1;
x |= x >> 1;
x |= x >> 2;
x |= x >> 4;
x |= x >> 8;
x |= x >> 16;
return x + 1;
}
/**
* Constructs a new {@code HashMap} instance with the specified capacity and
* load factor.
*
* @param capacity
* the initial capacity of this hash map.
* @param loadFactor
* the initial load factor.
* @throws IllegalArgumentException
* when the capacity is less than zero or the load factor is
* less or equal to zero.
*/
public HashMap(int capacity, float loadFactor) {
this.loadFactor = loadFactor;
init(capacity);
}
private void init(int capacity) {
if (capacity >= 0 && loadFactor > 0) {
capacity = calculateCapacity(capacity);
elementCount = 0;
elementData = newElementArray(capacity);
computeThreshold();
} else {
throw new IllegalArgumentException();
}
}
/**
* Removes all mappings from this hash map, leaving it empty.
*
* @see #isEmpty
* @see #size
*/
@Override
public void clear() {
if (elementCount > 0) {
elementCount = 0;
int length = elementData.length;
for (int i = 0; i < length; ++i)
elementData[i] = null;
modCount++;
}
}
/**
* Computes the threshold for rehashing
*/
private void computeThreshold() {
threshold = (int) (elementData.length * loadFactor);
}
/**
* Returns whether this map contains the specified key.
*
* @param key
* the key to search for.
* @return {@code true} if this map contains the specified key,
* {@code false} otherwise.
*/
@Override
public boolean containsKey(Object key) {
Entry<K, V> m = getEntry(key);
return m != null;
}
/**
* Returns whether this map contains the specified value.
*
* @param value
* the value to search for.
* @return {@code true} if this map contains the specified value,
* {@code false} otherwise.
*/
@Override
public boolean containsValue(Object value) {
if (value != null) {
for (int i = 0; i < elementData.length; i++) {
Entry<K, V> entry = elementData[i];
while (entry != null) {
if (areEqualValues(value, entry.value)) {
return true;
}
entry = entry.next;
}
}
} else {
for (int i = 0; i < elementData.length; i++) {
Entry<K, V> entry = elementData[i];
while (entry != null) {
if (entry.value == null) {
return true;
}
entry = entry.next;
}
}
}
return false;
}
/**
* Returns the value of the mapping with the specified key.
*
* @param key
* the key.
* @return the value of the mapping with the specified key, or {@code null}
* if no mapping for the specified key is found.
*/
@Override
public V get(Object key) {
Entry<K, V> m = getEntry(key);
if (m != null) {
return m.value;
}
return null;
}
final Entry<K, V> getEntry(Object key) {
Entry<K, V> m;
if (key == null) {
m = findNullKeyEntry();
} else {
int hash = computeHashCode(key);
int index = hash & (elementData.length - 1);
m = findNonNullKeyEntry(key, index, hash);
}
return m;
}
final Entry<K,V> findNonNullKeyEntry(Object key, int index, int keyHash) {
Entry<K,V> m = elementData[index];
while (m != null
&& (m.origKeyHash != keyHash || !areEqualKeys(key, m.key))) {
m = m.next;
}
return m;
}
final Entry<K,V> findNullKeyEntry() {
Entry<K,V> m = elementData[0];
while (m != null && m.key != null)
m = m.next;
return m;
}
/**
* Returns whether this map is empty.
*
* @return {@code true} if this map has no elements, {@code false}
* otherwise.
* @see #size()
*/
@Override
public boolean isEmpty() {
return elementCount == 0;
}
/**
* Maps the specified key to the specified value.
*
* @param key
* the key.
* @param value
* the value.
* @return the value of any previous mapping with the specified key or
* {@code null} if there was no such mapping.
*/
@Override
public V put(K key, V value) {
return putImpl(key, value);
}
V putImpl(K key, V value) {
Entry<K,V> entry;
if(key == null) {
entry = findNullKeyEntry();
if (entry == null) {
modCount++;
entry = createHashedEntry(null, 0, 0);
if (++elementCount > threshold) {
rehash();
}
}
} else {
int hash = computeHashCode(key);
int index = hash & (elementData.length - 1);
entry = findNonNullKeyEntry(key, index, hash);
if (entry == null) {
modCount++;
entry = createHashedEntry(key, index, hash);
if (++elementCount > threshold) {
rehash();
}
}
}
V result = entry.value;
entry.value = value;
return result;
}
Entry<K, V> createEntry(K key, int index, V value) {
Entry<K, V> entry = new Entry<K, V>(key, value);
entry.next = elementData[index];
elementData[index] = entry;
return entry;
}
Entry<K,V> createHashedEntry(K key, int index, int hash) {
Entry<K,V> entry = new Entry<K,V>(key,hash);
entry.next = elementData[index];
elementData[index] = entry;
return entry;
}
void rehash(int capacity) {
int length = calculateCapacity((capacity == 0 ? 1 : capacity << 1));
Entry<K, V>[] newData = newElementArray(length);
for (int i = 0; i < elementData.length; i++) {
Entry<K, V> entry = elementData[i];
elementData[i] = null;
while (entry != null) {
int index = entry.origKeyHash & (length - 1);
Entry<K, V> next = entry.next;
entry.next = newData[index];
newData[index] = entry;
entry = next;
}
}
elementData = newData;
computeThreshold();
}
void rehash() {
rehash(elementData.length);
}
/**
* Removes the mapping with the specified key from this map.
*
* @param key
* the key of the mapping to remove.
* @return the value of the removed mapping or {@code null} if no mapping
* for the specified key was found.
*/
@Override
public V remove(Object key) {
Entry<K, V> entry = removeEntry(key);
if (entry != null) {
return entry.value;
}
return null;
}
/*
* Remove the given entry from the hashmap.
* Assumes that the entry is in the map.
*/
final void removeEntry(Entry<K, V> entry) {
int index = entry.origKeyHash & (elementData.length - 1);
Entry<K, V> m = elementData[index];
if (m == entry) {
elementData[index] = entry.next;
} else {
while (m.next != entry) {
m = m.next;
}
m.next = entry.next;
}
modCount++;
elementCount--;
}
final Entry<K, V> removeEntry(Object key) {
int index = 0;
Entry<K, V> entry;
Entry<K, V> last = null;
if (key != null) {
int hash = computeHashCode(key);
index = hash & (elementData.length - 1);
entry = elementData[index];
while (entry != null && !(entry.origKeyHash == hash && areEqualKeys(key, entry.key))) {
last = entry;
entry = entry.next;
}
} else {
entry = elementData[0];
while (entry != null && entry.key != null) {
last = entry;
entry = entry.next;
}
}
if (entry == null) {
return null;
}
if (last == null) {
elementData[index] = entry.next;
} else {
last.next = entry.next;
}
modCount++;
elementCount--;
return entry;
}
/**
* Returns the number of elements in this map.
*
* @return the number of elements in this map.
*/
@Override
public int size() {
return elementCount;
}
/*
* Contract-related functionality
*/
static int computeHashCode(Object key) {
return key.hashCode();
}
static boolean areEqualKeys(Object key1, Object key2) {
return (key1 == key2) || key1.equals(key2);
}
static boolean areEqualValues(Object value1, Object value2) {
return (value1 == value2) || value1.equals(value2);
}
}