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package java.util; import java.io.*;public class Hashtable<K,V>extends Dictionary<K,V>implements Map<K,V>, Cloneable, java.io.Serializable {// Hashtable保存的是key-value的數組// Hashtbale是采用拉鏈法實現的，每一個Entry本質上是一個單向鏈表// 拉鏈法的本質：當散列表沖突時 ，我們重開一條鏈表。// transient 序列化時忽略該字段。// 數組存放的是實體的引用，序列化時必須遍歷該字段逐個實體序列化。private transient Entry[] table;// Hashtable中元素的實際數量private transient int count;// 擴容臨界值// 用于判斷是否需要調整Hashtable的容量(threshold=容量*加載因子)private int threshold;//加載因子private float loadFactor;// Hashtable被改變的次數private transient int modCount = 0;//序列版本號private static final long serialVersionUID = 1421746759512286392L;//指定容量大小和加載因子的構造方法public Hashtable(int initialCapacity, float loadFactor) {// 參數校驗if (initialCapacity < 0)throw new IllegalArgumentException("Illegal Capacity: "+ initialCapacity);if (loadFactor <= 0 || Float.isNaN(loadFactor))throw new IllegalArgumentException("Illegal Load: "+loadFactor);//如果初始化容量等于0，默認設置為1if (initialCapacity==0)initialCapacity = 1;//設置加載因子this.loadFactor = loadFactor;//創建存儲數組table = new Entry[initialCapacity];//設置擴容臨界值threshold = (int)(initialCapacity * loadFactor);}//指定容量大小的構造函數(構造因子默認是0.75f)public Hashtable(int initialCapacity) {this(initialCapacity, 0.75f);}//默認構造函數public Hashtable() {// 默認構造函數，指定大的容量大小是11；加載因子是0.75this(11, 0.75f);}//包含“子map”的構造函數public Hashtable(Map<? extends K, ? extends V> t) {this(Math.max(2*t.size(), 11), 0.75f);//將“子Map”的全部元素都添加到Hashtable中putAll(t);}//返回Hashtable存儲鍵值對的數目public synchronized int size() {return count;}// 判斷HashTable是否為空public synchronized boolean isEmpty() {return count == 0;}// 返回“所有key”的枚舉對象public synchronized Enumeration<K> keys() {return this.<K>getEnumeration(KEYS);}// 返回“所有的value”的枚舉對象public synchronized Enumeration<V> elements() {return this.<V>getEnumeration(VALUES);}// 判斷Hashtable是否包含“值(value)”public synchronized boolean contains(Object value) {// Hashtable中“鍵值對”的value不能是null，// 若是null的話，拋出異常!if (value == null) {throw new NullPointerException();}Entry tab[] = table;//從后向前遍歷table數組中的元素(entry)for (int i = tab.length ; i-- > 0 ;) {//對于每個Entry(單向鏈表)，逐個遍歷，判斷節點的值是否等于valuefor (Entry<K,V> e = tab[i] ; e != null ; e = e.next) {if (e.value.equals(value)) {return true;}}}return false;}// 判斷Hashtable是否包含“值(value)”public boolean containsValue(Object value) {return contains(value);}// 判斷Hashtable是否包含keypublic synchronized boolean containsKey(Object key) {Entry tab[] = table;int hash = key.hashCode();//計算索引值// % tab.length 是為了防止數組越界int index = (hash & 0x7FFFFFFF) % tab.length;// 找到“key對應的Entry(鏈表)”，然后在鏈表中找出“哈希值”和“鍵值”與key都相等的元素for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) {if ((e.hash == hash) && e.key.equals(key)) {return true;}}return false;}// 返回key對應的value，沒有的話返回nullpublic synchronized V get(Object key) {Entry tab[] = table;int hash = key.hashCode();//計算索引值int index = (hash & 0x7FFFFFFF) % tab.length;// 找到“key對應的Entry(鏈表)”，然后在鏈表中找出“哈希值”和“鍵值”與key都相等的元素for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) {if ((e.hash == hash) && e.key.equals(key)) {return e.value;}}return null;}//調整HashTable的長度，將長度變成原來的(2倍+1)protected void rehash() {//臨時保存舊容量，舊數據int oldCapacity = table.length;Entry[] oldMap = table;//創建新容量，新數據int newCapacity = oldCapacity * 2 + 1;Entry[] newMap = new Entry[newCapacity];//更新 修改次數、擴容臨界值、table數組modCount++;threshold = (int)(newCapacity * loadFactor);table = newMap;//將舊數組中的數據依次添加到新table數組中for (int i = oldCapacity ; i-- > 0 ;) {//添加鏈表for (Entry<K,V> old = oldMap[i] ; old != null ; ) {Entry<K,V> e = old;old = old.next;//計算擴容后的索引值int index = (e.hash & 0x7FFFFFFF) % newCapacity;e.next = newMap[index];newMap[index] = e;}}}// 將“key-value”鍵值對添加到Hashtable中public synchronized V put(K key, V value) {// HashTable中不能插入value為null的元素if (value == null) {throw new NullPointerException();}// 若HashTable中已存在鍵為key的鍵值對，// 則用新的value替換舊的valueEntry tab[] = table;int hash = key.hashCode();//計算索引值int index = (hash & 0x7FFFFFFF) % tab.length;// 根據索引遍歷對應的Entry鏈表for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) {if ((e.hash == hash) && e.key.equals(key)) {V old = e.value;e.value = value;return old;}}// 若HashTable中不存在鍵為key的鍵值對// 更新修改統計數modCount++;// 如果HashTable實際容量 > 擴容臨界值 (擴容臨界值=總容量*加載因子)// 則調整HashTable的大小if (count >= threshold) {// 擴容并按新容量設置hash分布rehash();//更具新容量計算索引tab = table;index = (hash & 0x7FFFFFFF) % tab.length;}// 將Hashtable中index位置的Entry(鏈表)保存到e中Entry<K,V> e = tab[index];// 將鍵值對插進entry鏈表中tab[index] = new Entry<K,V>(hash, key, value, e);// 實際容量+1count++;return null;}// 刪除Hashtable中鍵為key的元素public synchronized V remove(Object key) {Entry tab[] = table;int hash = key.hashCode();//計算索引值int index = (hash & 0x7FFFFFFF) % tab.length;// 根據索引遍歷對應的鏈表for (Entry<K,V> e = tab[index], prev = null ; e != null ; prev = e, e = e.next) {//找到要刪除的節點并刪除該節點if ((e.hash == hash) && e.key.equals(key)) {modCount++;if (prev != null) {prev.next = e.next;} else {tab[index] = e.next;}count--;V oldValue = e.value;e.value = null;return oldValue;}}return null;}// 將“Map t”中的全部元素注意添加到Hashtable中public synchronized void putAll(Map<? extends K, ? extends V> t) {for (Map.Entry<? extends K, ? extends V> e : t.entrySet())put(e.getKey(), e.getValue());}// 清空HashTable// 將HashTable的table數組的值全部設置為nullpublic synchronized void clear() {Entry tab[] = table;modCount++;//將引用設置為空for (int index = tab.length; --index >= 0; )tab[index] = null;count = 0;}// 克隆一個Hashtable，并以Object的形式返回。public synchronized Object clone() {try {Hashtable<K,V> t = (Hashtable<K,V>) super.clone();t.table = new Entry[table.length];for (int i = table.length ; i-- > 0 ; ) {t.table[i] = (table[i] != null)? (Entry<K,V>) table[i].clone() : null;}t.keySet = null;t.entrySet = null;t.values = null;t.modCount = 0;return t;} catch (CloneNotSupportedException e) {// this shouldn't happen, since we are Cloneablethrow new InternalError();}}public synchronized String toString() {int max = size() - 1;if (max == -1)return "{}";StringBuilder sb = new StringBuilder();Iterator<Map.Entry<K,V>> it = entrySet().iterator();sb.append('{');for (int i = 0; ; i++) {Map.Entry<K,V> e = it.next();K key = e.getKey();V value = e.getValue();sb.append(key == this ? "(this Map)" : key.toString());sb.append('=');sb.append(value == this ? "(this Map)" : value.toString());if (i == max)return sb.append('}').toString();sb.append(", ");}}// 獲取Hashtable的枚舉對象// 若Hashtable的實際大小為0，則返回“空枚舉類”對象// 否則，返回征程的Enumerator的對象。(Enumerator實現了迭代器和枚舉兩個接口)private <T> Enumeration<T> getEnumeration(int type) {if (count == 0) {return (Enumeration<T>)emptyEnumerator;} else {return new Enumerator<T>(type, false);}}// 獲取Hashtable的迭代器// 若Hashtable的實際大小為0，則返回空迭代器對象// 否則，返回正常的Enumerator的對象。(Enumerator實現了迭代器和枚舉兩個接口)private <T> Iterator<T> getIterator(int type) {if (count == 0) {return (Iterator<T>) emptyIterator;} else {return new Enumerator<T>(type, true);}}// Views// Hashtable的“key的集合”。它是一個set，意味著沒有重復元素private transient volatile Set<K> keySet = null;// Hashtable的“key-value集合”，元素不重復private transient volatile Set<Map.Entry<K,V>> entrySet = null;// Hashtable的"key-value集合"。它是一個Collection，有可能有重復private transient volatile Collection<V> values = null;// 返回一個被synchronizedSet封裝后的KeySet對象// synchronizedSet封裝的目的是實現多線程同步(對KeySet的所有方法都添加synchronized)public Set<K> keySet() {if (keySet == null)keySet = Collections.synchronizedSet(new KeySet(), this);return keySet;}// Hashtable的key的set集合// keySet繼承于AbstractSet，所以，keySet中的元素沒有重復private class KeySet extends AbstractSet<K> {public Iterator<K> iterator() {return getIterator(KEYS);}public int size() {return count;}public boolean contains(Object o) {return containsKey(o);}public boolean remove(Object o) {return Hashtable.this.remove(o) != null;}public void clear() {Hashtable.this.clear();}}// 返回一個被synchronizedSet封裝后的EntrySet對象// synchronizedSet封裝的目的實現多線程同步(對EntrySet的所有方法都添加synchronized)public Set<Map.Entry<K,V>> entrySet() {if (entrySet==null)entrySet = Collections.synchronizedSet(new EntrySet(), this);return entrySet;}// HashTabled的Entry的set集合// EntrySet繼承于AbstractSet，所以，EntrySet中的元素沒有重復的。private class EntrySet extends AbstractSet<Map.Entry<K,V>> {public Iterator<Map.Entry<K,V>> iterator() {return getIterator(ENTRIES);}public boolean add(Map.Entry<K,V> o) {return super.add(o);}// 是否包含目標對象public boolean contains(Object o) {// 如果o不是Map.Entry類型 則返回falseif (!(o instanceof Map.Entry))return false;Map.Entry entry = (Map.Entry)o;Object key = entry.getKey();Entry[] tab = table;int hash = key.hashCode();//計算索引值int index = (hash & 0x7FFFFFFF) % tab.length;//根據索引遍歷鏈表//查找鏈表中是否存在Object ofor (Entry e = tab[index]; e != null; e = e.next)if (e.hash==hash && e.equals(entry))return true;return false;}//刪除元素opublic boolean remove(Object o) {// 如果o不是Map.Entry類型 則返回falseif (!(o instanceof Map.Entry))return false;Map.Entry<K,V> entry = (Map.Entry<K,V>) o;K key = entry.getKey();Entry[] tab = table;int hash = key.hashCode();//計算索引值int index = (hash & 0x7FFFFFFF) % tab.length;//遍歷索引值對應的entry鏈表for (Entry<K,V> e = tab[index], prev = null; e != null;prev = e, e = e.next) {//找到刪除if (e.hash==hash && e.equals(entry)) {modCount++;if (prev != null)prev.next = e.next;elsetab[index] = e.next;count--;e.value = null;return true;}}return false;}public int size() {return count;}public void clear() {Hashtable.this.clear();}}// 返回一個被synchronizedCollection封裝后的ValueCollection對象// synchronizedCollection封裝的目的是實現多線程同步(對ValueCollection的所有方法都添加synchronized)public Collection<V> values() {if (values==null)values = Collections.synchronizedCollection(new ValueCollection(),this);return values;}// Hashtable的value的Collection集合。// ValueCollection繼承于AbstractCollection，所以，ValueCollection中的元素可以重復的。private class ValueCollection extends AbstractCollection<V> {public Iterator<V> iterator() {return getIterator(VALUES);}public int size() {return count;}public boolean contains(Object o) {return containsValue(o);}public void clear() {Hashtable.this.clear();}}// Comparison and hashing// 覆寫equals()方法// 若兩個Hashtable的所有key-value鍵值對都相等，則判斷它們兩個相等public synchronized boolean equals(Object o) {if (o == this)return true;if (!(o instanceof Map))return false;Map<K,V> t = (Map<K,V>) o;if (t.size() != size())return false;try {// 通過迭代器依次取出當前Hashtable的key-value鍵值對// 并判斷該鍵值對，存在于Hashtable(o)中。// 若不存在，則立即返回false；否則，遍歷完“當前Hashtable”并返回true。Iterator<Map.Entry<K,V>> i = entrySet().iterator();while (i.hasNext()) {Map.Entry<K,V> e = i.next();K key = e.getKey();V value = e.getValue();if (value == null) {if (!(t.get(key)==null && t.containsKey(key)))return false;} else {if (!value.equals(t.get(key)))return false;}}} catch (ClassCastException unused) {return false;} catch (NullPointerException unused) {return false;}return true;}// 計算Hashtable的哈希值public synchronized int hashCode() {int h = 0;// 若 Hashtable的實際大小為0 或者 加載因子<0，則返回0。if (count == 0 || loadFactor < 0)return h; // Returns zero// 否則，返回“Hashtable中的每個Entry的key和value的異或值 的總和”。loadFactor = -loadFactor; // Mark hashCode computation in progressEntry[] tab = table;for (int i = 0; i < tab.length; i++)for (Entry e = tab[i]; e != null; e = e.next)h += e.key.hashCode() ^ e.value.hashCode();loadFactor = -loadFactor; // Mark hashCode computation completereturn h;}// java.io.Serializable的寫入函數// 將Hashtable的“總的容量，實際容量，所有的Entry”都寫入到輸出流中private synchronized void writeObject(java.io.ObjectOutputStream s)throws IOException{// Write out the length, threshold, loadfactors.defaultWriteObject();// Write out length, count of elements and then the key/value objects// 寫入總容量s.writeInt(table.length);// 寫入實際容量s.writeInt(count);// 寫入所有實體數據for (int index = table.length-1; index >= 0; index--) {Entry entry = table[index];while (entry != null) {s.writeObject(entry.key);s.writeObject(entry.value);entry = entry.next;}}}// java.io.Serializable的讀取函數：根據寫入方式讀出// 將Hashtable的“總的容量，實際容量，所有的Entry”依次讀出private void readObject(java.io.ObjectInputStream s)throws IOException, ClassNotFoundException{// Read in the length, threshold, and loadfactors.defaultReadObject();// Read the original length of the array and number of elements//讀取總容量int origlength = s.readInt();//讀取實際容量int elements = s.readInt();// Compute new size with a bit of room 5% to grow but// no larger than the original size. Make the length// odd if it's large enough, this helps distribute the entries.// Guard against the length ending up zero, that's not valid.int length = (int)(elements * loadFactor) + (elements / 20) + 3;if (length > elements && (length & 1) == 0)length--;if (origlength > 0 && length > origlength)length = origlength;Entry[] table = new Entry[length];count = 0;// Read the number of elements and then all the key/value objects// 讀取所有entry實體數據for (; elements > 0; elements--) {K key = (K)s.readObject();V value = (V)s.readObject();// synch could be eliminated for performancereconstitutionPut(table, key, value);}this.table = table;}// 重建Entry[] table數組，只有readObject調用該方法private void reconstitutionPut(Entry[] tab, K key, V value)throws StreamCorruptedException{if (value == null) {throw new java.io.StreamCorruptedException();}// Makes sure the key is not already in the hashtable.// This should not happen in deserialized version.int hash = key.hashCode();int index = (hash & 0x7FFFFFFF) % tab.length;for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) {if ((e.hash == hash) && e.key.equals(key)) {throw new java.io.StreamCorruptedException();}}// Creates the new entry.Entry<K,V> e = tab[index];tab[index] = new Entry<K,V>(hash, key, value, e);count++;}// Hashtable的Entry節點，它本質上是一個單向鏈表。// 因此，我們才能推斷出Hashtable是由拉鏈法實現的散列表private static class Entry<K,V> implements Map.Entry<K,V> {// 哈希值int hash;K key;V value;// 指向的下一個Entry，即鏈表的下一個節點Entry<K,V> next;// 構造函數protected Entry(int hash, K key, V value, Entry<K,V> next) {this.hash = hash;this.key = key;this.value = value;this.next = next;}protected Object clone() {return new Entry<K,V>(hash, key, value,(next==null ? null : (Entry<K,V>) next.clone()));}// Map.Entry Opspublic K getKey() {return key;}public V getValue() {return value;}//設置value。若value是null，則拋出異常public V setValue(V value) {if (value == null)throw new NullPointerException();V oldValue = this.value;this.value = value;return oldValue;}// 覆蓋equals()方法，判斷兩個Entry是否相等。// 若兩個Entry的key和value都相等，則認為它們相等。public boolean equals(Object o) {if (!(o instanceof Map.Entry))return false;Map.Entry e = (Map.Entry)o;return (key==null ? e.getKey()==null : key.equals(e.getKey())) &&(value==null ? e.getValue()==null : value.equals(e.getValue()));}public int hashCode() {return hash ^ (value==null ? 0 : value.hashCode());}public String toString() {return key.toString()+"="+value.toString();} }// Types of Enumerations/Iterationsprivate static final int KEYS = 0;private static final int VALUES = 1;private static final int ENTRIES = 2;// Enumerator的作用是提供了“通過elements()遍歷Hashtable的接口” 和 “通過entrySet()遍歷Hashtable的接口”。// 因為，它同時實現了 “Enumerator接口”和“Iterator接口”。private class Enumerator<T> implements Enumeration<T>, Iterator<T> {// 指向Hashtable的tableEntry[] table = Hashtable.this.table;// Hashtable的總容量int index = table.length;Entry<K,V> entry = null;Entry<K,V> lastReturned = null;int type;// Enumerator是 “迭代器(Iterator)” 還是 “枚舉類(Enumeration)”的標志// iterator為true，表示它是迭代器；否則，是枚舉類。boolean iterator;// 在將Enumerator當作迭代器使用時會用到，用來實現fail-fast機制。protected int expectedModCount = modCount;Enumerator(int type, boolean iterator) {this.type = type;this.iterator = iterator;}// 從遍歷table的數組的末尾向前查找，// 直到找到不為null的Entry。public boolean hasMoreElements() {Entry<K,V> e = entry;//index初始值為數組長度int i = index;Entry[] t = table;/* Use locals for faster loop iteration *///從尾向頭遍歷while (e == null && i > 0) {e = t[--i];}entry = e;index = i;return e != null;}// 獲取下一個元素// 注意：從hasMoreElements() 和nextElement() // 可以看出“Hashtable的elements()遍歷方式”// 首先，從后向前的遍歷table數組。table數組的每個節點都是一個單向鏈表(Entry)。// 然后，依次向后遍歷單向鏈表Entry。public T nextElement() {Entry<K,V> et = entry;//index初始值為數組長度int i = index;Entry[] t = table;/* Use locals for faster loop iteration *///從后向前遍歷while (et == null && i > 0) {et = t[--i];}entry = et;index = i;if (et != null) {Entry<K,V> e = lastReturned = entry;entry = e.next;return type == KEYS ? (T)e.key : (type == VALUES ? (T)e.value : (T)e);}throw new NoSuchElementException("Hashtable Enumerator");}// 迭代器Iterator的判斷是否存在下一個元素// 實際上，它是調用的hasMoreElements()public boolean hasNext() {return hasMoreElements();}// 迭代器獲取下一個元素// 實際上，它是調用的nextElement()public T next() {if (modCount != expectedModCount)throw new ConcurrentModificationException();return nextElement();}// 迭代器的remove()接口。// 首先，它在table數組中找出要刪除元素所在的Entry，// 然后，刪除單向鏈表Entry中的元素public void remove() {if (!iterator)throw new UnsupportedOperationException();if (lastReturned == null)throw new IllegalStateException("Hashtable Enumerator");if (modCount != expectedModCount)throw new ConcurrentModificationException();synchronized(Hashtable.this) {Entry[] tab = Hashtable.this.table;//刪除lastReturned，計算索引int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length;//遍歷列表刪除for (Entry<K,V> e = tab[index], prev = null; e != null;prev = e, e = e.next) {if (e == lastReturned) {modCount++;expectedModCount++;if (prev == null)tab[index] = e.next;elseprev.next = e.next;count--;lastReturned = null;return;}}throw new ConcurrentModificationException();}}}private static Enumeration emptyEnumerator = new EmptyEnumerator();private static Iterator emptyIterator = new EmptyIterator();// 空枚舉類// 當Hashtable的實際大小為0；此時，// 又要通過Enumeration遍歷Hashtable時，返回的是“空枚舉類”的對象。private static class EmptyEnumerator implements Enumeration<Object> {EmptyEnumerator() {}// 空枚舉類的hasMoreElements() 始終返回falsepublic boolean hasMoreElements() {return false;}// 空枚舉類的nextElement() 拋出異常public Object nextElement() {throw new NoSuchElementException("Hashtable Enumerator");}}// 空迭代器// 當Hashtable的實際大小為0；此時，// 又要通過迭代器遍歷Hashtable時，返回的是“空迭代器”的對象。private static class EmptyIterator implements Iterator<Object> {EmptyIterator() {}//空迭代器的hasNext，始終返回falsepublic boolean hasNext() {return false;}//空迭代器的next，拋出異常public Object next() {throw new NoSuchElementException("Hashtable Iterator");}public void remove() {throw new IllegalStateException("Hashtable Iterator");}}}

轉載于:https://my.oschina.net/u/140462/blog/198354

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