org.eclipse.jface.viewers.CustomHashtable Maven / Gradle / Ivy
/*******************************************************************************
* Copyright (c) 2000, 2017 IBM Corporation and others.
*
* This program and the accompanying materials
* are made available under the terms of the Eclipse Public License 2.0
* which accompanies this distribution, and is available at
* https://www.eclipse.org/legal/epl-2.0/
*
* SPDX-License-Identifier: EPL-2.0
*
* Contributors:
* Peter Shipton - original hashtable implementation
* Nick Edgar - added element comparer support
*******************************************************************************/
package org.eclipse.jface.viewers;
import java.util.Enumeration;
import java.util.NoSuchElementException;
/**
* CustomHashtable associates keys with values. Keys and values cannot be null.
* The size of the Hashtable is the number of key/value pairs it contains.
* The capacity is the number of key/value pairs the Hashtable can hold.
* The load factor is a float value which determines how full the Hashtable
* gets before expanding the capacity. If the load factor of the Hashtable
* is exceeded, the capacity is doubled.
*
* CustomHashtable allows a custom comparator and hash code provider.
*/
/* package */final class CustomHashtable {
/**
* HashMapEntry is an internal class which is used to hold the entries of a Hashtable.
*/
private static class HashMapEntry {
Object key, value;
HashMapEntry next;
HashMapEntry(Object theKey, Object theValue) {
key = theKey;
value = theValue;
}
}
private static final class EmptyEnumerator implements Enumeration {
@Override
public boolean hasMoreElements() {
return false;
}
@Override
public Object nextElement() {
throw new NoSuchElementException();
}
}
private class HashEnumerator implements Enumeration {
boolean key;
int start;
HashMapEntry entry;
HashEnumerator(boolean isKey) {
key = isKey;
start = firstSlot;
}
@Override
public boolean hasMoreElements() {
if (entry != null) {
return true;
}
while (start <= lastSlot) {
if (elementData[start++] != null) {
entry = elementData[start - 1];
return true;
}
}
return false;
}
@Override
public Object nextElement() {
if (hasMoreElements()) {
Object result = key ? entry.key : entry.value;
entry = entry.next;
return result;
}
throw new NoSuchElementException();
}
}
transient int elementCount;
transient HashMapEntry[] elementData;
private float loadFactor;
private int threshold;
transient int firstSlot = 0;
transient int lastSlot = -1;
transient private IElementComparer comparer;
private static final EmptyEnumerator emptyEnumerator = new EmptyEnumerator();
/**
* The default capacity used when not specified in the constructor.
*/
public static final int DEFAULT_CAPACITY = 13;
/**
* Constructs a new Hashtable using the default capacity
* and load factor.
*/
public CustomHashtable() {
this(13);
}
/**
* Constructs a new Hashtable using the specified capacity
* and the default load factor.
*
* @param capacity the initial capacity
*/
public CustomHashtable(int capacity) {
this(capacity, null);
}
/**
* Constructs a new hash table with the default capacity and the given
* element comparer.
*
* @param comparer the element comparer to use to compare keys and obtain
* hash codes for keys, or null to use the normal
* equals and hashCode methods
*/
public CustomHashtable(IElementComparer comparer) {
this(DEFAULT_CAPACITY, comparer);
}
/**
* Constructs a new hash table with the given capacity and the given
* element comparer.
*
* @param capacity the maximum number of elements that can be added without
* rehashing
* @param comparer the element comparer to use to compare keys and obtain
* hash codes for keys, or null to use the normal
* equals and hashCode methods
*/
public CustomHashtable(int capacity, IElementComparer comparer) {
if (capacity >= 0) {
elementCount = 0;
elementData = new HashMapEntry[capacity == 0 ? 1 : capacity];
firstSlot = elementData.length;
loadFactor = 0.75f;
computeMaxSize();
} else {
throw new IllegalArgumentException();
}
this.comparer = comparer;
}
/**
* Constructs a new hash table with enough capacity to hold all keys in the
* given hash table, then adds all key/value pairs in the given hash table
* to the new one, using the given element comparer.
* @param table the original hash table to copy from
*
* @param comparer the element comparer to use to compare keys and obtain
* hash codes for keys, or null to use the normal
* equals and hashCode methods
*/
public CustomHashtable(CustomHashtable table, IElementComparer comparer) {
this(table.size() * 2, comparer);
for (int i = table.elementData.length; --i >= 0;) {
HashMapEntry entry = table.elementData[i];
while (entry != null) {
put(entry.key, entry.value);
entry = entry.next;
}
}
}
/**
* Returns the element comparer used to compare keys and to obtain
* hash codes for keys, or null if no comparer has been
* provided.
*
* @return the element comparer or null
*
* @since 3.2
*/
public IElementComparer getComparer() {
return comparer;
}
private void computeMaxSize() {
threshold = (int) (elementData.length * loadFactor);
}
/**
* Answers if this Hashtable contains the specified object as a key
* of one of the key/value pairs.
*
* @param key the object to look for as a key in this Hashtable
* @return true if object is a key in this Hashtable, false otherwise
*/
public boolean containsKey(Object key) {
return getEntry(key) != null;
}
/**
* Answers an Enumeration on the values of this Hashtable. The
* results of the Enumeration may be affected if the contents
* of this Hashtable are modified.
*
* @return an Enumeration of the values of this Hashtable
*/
public Enumeration elements() {
if (elementCount == 0) {
return emptyEnumerator;
}
return new HashEnumerator(false);
}
/**
* Answers the value associated with the specified key in
* this Hashtable.
*
* @param key the key of the value returned
* @return the value associated with the specified key, null if the specified key
* does not exist
*/
public Object get(Object key) {
int index = (hashCode(key) & 0x7FFFFFFF) % elementData.length;
HashMapEntry entry = elementData[index];
while (entry != null) {
if (keyEquals(key, entry.key)) {
return entry.value;
}
entry = entry.next;
}
return null;
}
private HashMapEntry getEntry(Object key) {
int index = (hashCode(key) & 0x7FFFFFFF) % elementData.length;
HashMapEntry entry = elementData[index];
while (entry != null) {
if (keyEquals(key, entry.key)) {
return entry;
}
entry = entry.next;
}
return null;
}
/**
* Answers the hash code for the given key.
*/
private int hashCode(Object key) {
if (comparer == null) {
return key.hashCode();
}
return comparer.hashCode(key);
}
/**
* Compares two keys for equality.
*/
private boolean keyEquals(Object a, Object b) {
if (comparer == null) {
return a.equals(b);
}
return comparer.equals(a, b);
}
/**
* Answers an Enumeration on the keys of this Hashtable. The
* results of the Enumeration may be affected if the contents
* of this Hashtable are modified.
*
* @return an Enumeration of the keys of this Hashtable
*/
public Enumeration keys() {
if (elementCount == 0) {
return emptyEnumerator;
}
return new HashEnumerator(true);
}
/**
* Associate the specified value with the specified key in this Hashtable.
* If the key already exists, the old value is replaced. The key and value
* cannot be null.
*
* @param key the key to add
* @param value the value to add
* @return the old value associated with the specified key, null if the key did
* not exist
*/
public Object put(Object key, Object value) {
if (key != null && value != null) {
int index = (hashCode(key) & 0x7FFFFFFF) % elementData.length;
HashMapEntry entry = elementData[index];
while (entry != null && !keyEquals(key, entry.key)) {
entry = entry.next;
}
if (entry == null) {
if (++elementCount > threshold) {
rehash();
index = (hashCode(key) & 0x7FFFFFFF) % elementData.length;
}
if (index < firstSlot) {
firstSlot = index;
}
if (index > lastSlot) {
lastSlot = index;
}
entry = new HashMapEntry(key, value);
entry.next = elementData[index];
elementData[index] = entry;
return null;
}
Object result = entry.value;
entry.key = key; // important to avoid hanging onto keys that are equal but "old" -- see bug 30607
entry.value = value;
return result;
}
throw new NullPointerException();
}
/**
* Increases the capacity of this Hashtable. This method is sent when
* the size of this Hashtable exceeds the load factor.
*/
private void rehash() {
int length = elementData.length << 1;
if (length == 0) {
length = 1;
}
firstSlot = length;
lastSlot = -1;
HashMapEntry[] newData = new HashMapEntry[length];
for (int i = elementData.length; --i >= 0;) {
HashMapEntry entry = elementData[i];
while (entry != null) {
int index = (hashCode(entry.key) & 0x7FFFFFFF) % length;
if (index < firstSlot) {
firstSlot = index;
}
if (index > lastSlot) {
lastSlot = index;
}
HashMapEntry next = entry.next;
entry.next = newData[index];
newData[index] = entry;
entry = next;
}
}
elementData = newData;
computeMaxSize();
}
/**
* Remove the key/value pair with the specified key from this Hashtable.
*
* @param key the key to remove
* @return the value associated with the specified key, null if the specified key
* did not exist
*/
public Object remove(Object key) {
HashMapEntry last = null;
int index = (hashCode(key) & 0x7FFFFFFF) % elementData.length;
HashMapEntry entry = elementData[index];
while (entry != null && !keyEquals(key, entry.key)) {
last = entry;
entry = entry.next;
}
if (entry != null) {
if (last == null) {
elementData[index] = entry.next;
} else {
last.next = entry.next;
}
elementCount--;
return entry.value;
}
return null;
}
/**
* Answers the number of key/value pairs in this Hashtable.
*
* @return the number of key/value pairs in this Hashtable
*/
public int size() {
return elementCount;
}
@Override
public String toString() {
if (size() == 0) {
return "{}"; //$NON-NLS-1$
}
StringBuilder buffer = new StringBuilder();
buffer.append('{');
for (int i = elementData.length; --i >= 0;) {
HashMapEntry entry = elementData[i];
while (entry != null) {
buffer.append(entry.key);
buffer.append('=');
buffer.append(entry.value);
buffer.append(", "); //$NON-NLS-1$
entry = entry.next;
}
}
// Remove the last ", "
if (elementCount > 0) {
buffer.setLength(buffer.length() - 2);
}
buffer.append('}');
return buffer.toString();
}
}