Java tutorial
/* * Copyright (c) 1998 - 2005 Versant Corporation * All rights reserved. This program and the accompanying materials * are made available under the terms of the Eclipse Public License v1.0 * which accompanies this distribution, and is available at * http://www.eclipse.org/legal/epl-v10.html * * Contributors: * Versant Corporation - initial API and implementation */ import java.io.IOException; import java.io.Serializable; /** * Specialized HashMap mapping int to Object. This is a cut and paste of * java.util.HashMap with the key hardcoded as int and some non-required * functionality removed. */ public final class IntObjectHashMap implements Serializable { /** * The default initial capacity - MUST be a power of two. */ private static final int DEFAULT_INITIAL_CAPACITY = 16; /** * The maximum capacity, used if a higher value is implicitly specified * by either of the constructors with arguments. * MUST be a power of two <= 1<<30. */ private static final int MAXIMUM_CAPACITY = 1 << 30; /** * The load factor used when none specified in constructor. */ private static final float DEFAULT_LOAD_FACTOR = 0.75f; /** * The table, resized as necessary. Length MUST Always be a power of two. */ private transient Entry[] table; /** * The number of key-value mappings contained in this identity hash map. */ private transient int size; /** * The next size value at which to resize (capacity * load factor). * * @serial */ private int threshold; /** * The load factor for the hash table. * * @serial */ private final float loadFactor; /** * Constructs an empty <tt>IntObjectHashMap</tt> with the specified initial * capacity and load factor. * * @param initialCapacity The initial capacity. * @param loadFactor The load factor. * @throws IllegalArgumentException if the initial capacity is negative * or the load factor is nonpositive. */ public IntObjectHashMap(int initialCapacity, float loadFactor) { if (initialCapacity < 0) { throw new IllegalArgumentException("Illegal initial capacity: " + initialCapacity); } if (initialCapacity > MAXIMUM_CAPACITY) { initialCapacity = MAXIMUM_CAPACITY; } if (loadFactor <= 0 || Float.isNaN(loadFactor)) { throw new IllegalArgumentException("Illegal load factor: " + loadFactor); } // Find a power of 2 >= initialCapacity int capacity = 1; while (capacity < initialCapacity) { capacity <<= 1; } this.loadFactor = loadFactor; threshold = (int) (capacity * loadFactor); table = new Entry[capacity]; } /** * Constructs an empty <tt>IntObjectHashMap</tt> with the specified initial * capacity and the default load factor (0.75). * * @param initialCapacity the initial capacity. * @throws IllegalArgumentException if the initial capacity is negative. */ public IntObjectHashMap(int initialCapacity) { this(initialCapacity, DEFAULT_LOAD_FACTOR); } /** * Constructs an empty <tt>IntObjectHashMap</tt> with the default initial capacity * (16) and the default load factor (0.75). */ public IntObjectHashMap() { this.loadFactor = DEFAULT_LOAD_FACTOR; threshold = (int) (DEFAULT_INITIAL_CAPACITY * DEFAULT_LOAD_FACTOR); table = new Entry[DEFAULT_INITIAL_CAPACITY]; } /** * Returns a string representation of this map. The string representation * consists of a list of key-value mappings in the order returned by the * map's <tt>entrySet</tt> view's iterator, enclosed in braces * (<tt>"{}"</tt>). Adjacent mappings are separated by the characters * <tt>", "</tt> (comma and space). Each key-value mapping is rendered as * the key followed by an equals sign (<tt>"="</tt>) followed by the * associated value. Keys and values are converted to strings as by * <tt>String.valueOf(Object)</tt>.<p> * <p/> * This implementation creates an empty string buffer, appends a left * brace, and iterates over the map's <tt>entrySet</tt> view, appending * the string representation of each <tt>map.entry</tt> in turn. After * appending each entry except the last, the string <tt>", "</tt> is * appended. Finally a right brace is appended. A string is obtained * from the stringbuffer, and returned. * * @return a String representation of this map. */ public String toString() { StringBuffer buf = new StringBuffer(); buf.append("{"); for (int i = 0; i < table.length; i++) { Entry e = table[i]; for (; e != null; e = e.next) { int key = e.key; Object value = e.getValue(); buf.append(key + "=" + (value == this ? "(this Map)" : value)); } } buf.append("}"); return buf.toString(); } /** * Returns the number of key-value mappings in this map. * * @return the number of key-value mappings in this map. */ public int size() { return size; } /** * Returns <tt>true</tt> if this map contains no key-value mappings. * * @return <tt>true</tt> if this map contains no key-value mappings. */ public boolean isEmpty() { return size == 0; } /** * Returns the value to which the specified key is mapped in this identity * hash map, or <tt>null</tt> if the map contains no mapping for this key. * A return value of <tt>null</tt> does not <i>necessarily</i> indicate * that the map contains no mapping for the key; it is also possible that * the map explicitly maps the key to <tt>null</tt>. The * <tt>containsKey</tt> method may be used to distinguish these two cases. * * @param key the key whose associated value is to be returned. * @return the value to which this map maps the specified key, or * <tt>null</tt> if the map contains no mapping for this key. */ public Object get(int key) { int i = key & (table.length - 1); Entry e = table[i]; while (true) { if (e == null) { return e; } if (key == e.key) { return e.value; } e = e.next; } } /** * Returns <tt>true</tt> if this map contains a mapping for the * specified key. * * @param key The key whose presence in this map is to be tested * @return <tt>true</tt> if this map contains a mapping for the specified * key. */ public boolean containsKey(int key) { int i = key & (table.length - 1); Entry e = table[i]; while (e != null) { if (key == e.key) { return true; } e = e.next; } return false; } /** * Associates the specified value with the specified key in this map. * If the map previously contained a mapping for this key, the old * value is replaced. * * @param key key with which the specified value is to be associated. * @param value value to be associated with the specified key. * @return previous value associated with specified key, or <tt>null</tt> * if there was no mapping for key. A <tt>null</tt> return can * also indicate that the IntObjectHashMap previously associated * <tt>null</tt> with the specified key. */ public Object put(int key, Object value) { int i = key & (table.length - 1); for (Entry e = table[i]; e != null; e = e.next) { if (key == e.key) { Object oldValue = e.value; e.value = value; return oldValue; } } addEntry(key, value, i); return null; } /** * This method is used instead of put by constructors and * pseudoconstructors (clone, readObject). It does not resize the table, * check for comodification, etc. It calls createEntry rather than * addEntry. */ private void putForCreate(int key, Object value) { int i = key & (table.length - 1); /** * Look for preexisting entry for key. This will never happen for * clone or deserialize. It will only happen for construction if the * input Map is a sorted map whose ordering is inconsistent w/ equals. */ for (Entry e = table[i]; e != null; e = e.next) { if (key == e.key) { e.value = value; return; } } createEntry(key, value, i); } /** * Rehashes the contents of this map into a new array with a * larger capacity. This method is called automatically when the * number of keys in this map reaches its threshold. * <p/> * If current capacity is MAXIMUM_CAPACITY, this method does not * resize the map, but but sets threshold to Integer.MAX_VALUE. * This has the effect of preventing future calls. * * @param newCapacity the new capacity, MUST be a power of two; * must be greater than current capacity unless current * capacity is MAXIMUM_CAPACITY (in which case value * is irrelevant). */ private void resize(int newCapacity) { Entry[] oldTable = table; int oldCapacity = oldTable.length; if (oldCapacity == MAXIMUM_CAPACITY) { threshold = Integer.MAX_VALUE; return; } Entry[] newTable = new Entry[newCapacity]; transfer(newTable); table = newTable; threshold = (int) (newCapacity * loadFactor); } /** * Transfer all entries from current table to newTable. */ private void transfer(Entry[] newTable) { Entry[] src = table; int newCapacity = newTable.length; for (int j = 0; j < src.length; j++) { Entry e = src[j]; if (e != null) { src[j] = null; do { Entry next = e.next; int i = e.key & (newCapacity - 1); e.next = newTable[i]; newTable[i] = e; e = next; } while (e != null); } } } /** * Removes the mapping for this key from this map if present. * * @param key key whose mapping is to be removed from the map. * @return previous value associated with specified key, or <tt>null</tt> * if there was no mapping for key. A <tt>null</tt> return can * also indicate that the map previously associated <tt>null</tt> * with the specified key. */ public Object remove(int key) { Entry e = removeEntryForKey(key); return e == null ? e : e.value; } /** * Removes and returns the entry associated with the specified key * in the IntObjectHashMap. Returns null if the IntObjectHashMap contains no mapping * for this key. */ private Entry removeEntryForKey(int key) { int i = key & (table.length - 1); Entry prev = table[i]; Entry e = prev; while (e != null) { Entry next = e.next; if (key == e.key) { size--; if (prev == e) { table[i] = next; } else { prev.next = next; } return e; } prev = e; e = next; } return e; } /** * Removes all mappings from this map. */ public void clear() { Entry tab[] = table; for (int i = 0; i < tab.length; i++) { tab[i] = null; } size = 0; } /** * Returns <tt>true</tt> if this map maps one or more keys to the * specified value. * * @param value value whose presence in this map is to be tested. * @return <tt>true</tt> if this map maps one or more keys to the * specified value. */ public boolean containsValue(Object value) { Entry tab[] = table; for (int i = 0; i < tab.length; i++) { for (Entry e = tab[i]; e != null; e = e.next) { if (value.equals(e.value)) { return true; } } } return false; } private static class Entry { final int key; Object value; Entry next; /** * Create new entry. */ public Entry(int k, Object v, Entry n) { value = v; next = n; key = k; } public Object getValue() { return value; } public Object setValue(Object newValue) { Object oldValue = value; value = newValue; return oldValue; } public boolean equals(Object o) { if (!(o instanceof Entry)) { return false; } Entry e = (Entry) o; if (key == e.key) { if (value == e.value || (value != null && value.equals(e.value))) { return true; } } return false; } public int hashCode() { return key ^ (value == null ? 0 : value.hashCode()); } public String toString() { return key + "=" + getValue(); } } /** * Add a new entry with the specified key, value and hash code to * the specified bucket. It is the responsibility of this * method to resize the table if appropriate. * <p/> * Subclass overrides this to alter the behavior of put method. */ private void addEntry(int key, Object value, int bucketIndex) { table[bucketIndex] = new Entry(key, value, table[bucketIndex]); if (size++ >= threshold) { resize(2 * table.length); } } /** * Like addEntry except that this version is used when creating entries * as part of Map construction or "pseudo-construction" (cloning, * deserialization). This version needn't worry about resizing the table. * <p/> * Subclass overrides this to alter the behavior of IntObjectHashMap(Map), * clone, and readObject. */ private void createEntry(int key, Object value, int bucketIndex) { table[bucketIndex] = new Entry(key, value, table[bucketIndex]); size++; } /** * Save the state of the <tt>IntObjectHashMap</tt> instance to a stream (i.e., * serialize it). * * @serialData The <i>capacity</i> of the IntObjectHashMap (the length of the * bucket array) is emitted (int), followed by the * <i>size</i> of the IntObjectHashMap (the number of key-value * mappings), followed by the key (Object) and value (Object) * for each key-value mapping represented by the IntObjectHashMap * The key-value mappings are emitted in the order that they * are returned by <tt>entrySet().iterator()</tt>. */ private void writeObject(java.io.ObjectOutputStream s) throws IOException { // Write out the threshold, loadfactor, and any hidden stuff s.defaultWriteObject(); // Write out number of buckets s.writeInt(table.length); // Write out size (number of Mappings) s.writeInt(size); // Write out keys and values (alternating) int c = 0; for (int i = 0; c < size && i < table.length; i++) { Entry e = table[i]; for (; e != null; e = e.next, ++c) { s.writeInt(e.key); s.writeObject(e.getValue()); } } } /** * Reconstitute the <tt>IntObjectHashMap</tt> instance from a stream (i.e., * deserialize it). */ private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException { // Read in the threshold, loadfactor, and any hidden stuff s.defaultReadObject(); // Read in number of buckets and allocate the bucket array; int numBuckets = s.readInt(); table = new Entry[numBuckets]; // Read in size (number of Mappings) int size = s.readInt(); // Read the keys and values, and put the mappings in the IntObjectHashMap for (int i = 0; i < size; i++) { int key = s.readInt(); Object value = s.readObject(); putForCreate(key, value); } } }