Java集合之詳細介紹Hashtable（圖文）
- 黄舟原創
- 2017-03-13 17:43:502058瀏覽
和HashMap一樣，Hashtable也是散列表，儲存的內容也是鍵值對key-value映射。它繼承了Dictionary，並實作了Map、Cloneable、io、Serializable介面。 Hashtable是線程安全的，並且key和value不能為空，並且不是有序的。
Hashtable有兩個參數影響其效能：初始容量和載入因子。容量是哈希表中桶的數量，初始容量就是哈希表創建時的容量，加載因子是對哈希表在其容量自動增加之前可以達到多滿的一個尺度。預設的載入因子是0.75。
Hashtable結構圖：
#從圖中可以看出：
（1）Hashtable繼承於Dictionary類，實作了Map介面。
（2）Hashtable透過拉鍊法（對衝突的採用鍊錶的方式）實現的雜湊表。包括幾個重要的成員變數：
table是一個Entry[]陣列類型，Entry是一個單向鍊錶，雜湊表的key-value都儲存在Entry數組中的。
count是Hashtable的大小，是Hashtable保存鍵值對的數量。
threshold是Hashtable的閾值，用於判斷是否需要調整Hashtable的容量，threshold的值=容量乘以加載因子。
loadFactor是載重因數。
modCount是用來實現fail-fast機制的。
Hashtable遍歷方式：
（1）遍歷Hashtable的鍵值對：首先取得Hashtable的鍵值對set#集合，之後透過迭代器對集合進行迭代遍歷。
Integer integ = Iterator iter = table.entrySet().iterator()(iter.hasNext())
{
Map.Entry entry = (Map.Entry)iter.next() key = (String)entry.getKey() integ = (Integer)entry.getValue()}
（2）遍歷Hashtable的鍵：透過keySet()取得鍵集合，透過Iterator迭代器遍歷得到值。
String key = Integer integ = Iterator iter = table.keySet().iterator()(iter.hasNext()) {
key = (String)iter.next() integ = (Integer)table.get(key)}
（3）遍歷Hashtable的值：透過values()得到Hashtable的值集合，透過Iterator迭代器遍歷獲得值
Integer value = Collection c = table.values()Iterator iter= c.iterator()(iter.hasNext())
{
value = (Integer)iter.next()}
（4）透過Enumeration遍歷Hashtable的鍵或值：先取得鍵或值的集合，透過Enumeration遍歷得到值。
Enumeration enu = table.keys()(enu.hasMoreElements())
{
System.out.println(enu.nextElement())}
Enumeration enu = table.elements()(enu.hasMoreElements())
{
System.out.println(enu.nextElement())}
Hashtable範例程式碼：
public class Hello {
public static void main(String[] args) {
testHashtableAPIs();
}
private static void testHashtableAPIs() {
// 初始化随机种子
Random r = new Random();
// 新建Hashtable
Hashtable table = new Hashtable();
// 添加操作
table.put("one", r.nextInt(10));
table.put("two", r.nextInt(10));
table.put("three", r.nextInt(10));
// 打印出table
System.out.println("table:"+table );
// 通过Iterator遍历key-value
Iterator iter = table.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry entry = (Map.Entry)iter.next();
System.out.println("next : "+ entry.getKey() +" - "+entry.getValue());
}
// Hashtable的键值对个数
System.out.println("size:"+table.size());
// containsKey(Object key) :是否包含键key
System.out.println("contains key two : "+table.containsKey("two"));
System.out.println("contains key five : "+table.containsKey("five"));
// containsValue(Object value) :是否包含值value
System.out.println("contains value 0 : "+table.containsValue(new Integer(0)));
// remove(Object key) ： 删除键key对应的键值对
table.remove("three");
System.out.println("table:"+table );
// clear() ： 清空Hashtable
table.clear();
// isEmpty() : Hashtable是否为空
System.out.println((table.isEmpty()?"table is empty":"table is not empty") );
}
}
執行結果：
table:{two=5, one=4, three=2}
next : two - 5
next : one - 4
next : three - 2
size:3
contains key two : true
contains key five : false
contains value 0 : false
table:{two=5, one=4}
table is empty#基於Java8的Dictionary原始碼：
Dictionarya8093152e673feb7aba1828c43532094 {
Dictionary() {
}
()()Enumerationa8093152e673feb7aba1828c43532094 ()Enumerationa8093152e673feb7aba1828c43532094 ()(Object key)(keyvalue)(Object key)}
基於Java8的Hashtable原始碼：
##
public class Hashtableb77a8d9c3c319e50d4b02a976b347910
extends Dictionaryb77a8d9c3c319e50d4b02a976b347910
implements Mapb77a8d9c3c319e50d4b02a976b347910, Cloneable, java.io.Serializable {
/**
* The hash table data.
*/
private transient Entryc3f2d894ed311a524f031af7191b9ddc[] table;//entry表
/**
* The total number of entries in the hash table.
*/
private transient int count;//entry数据
/**
* The table is rehashed when its size exceeds this threshold. (The
* value of this field is (int)(capacity * loadFactor).)
*
* @serial
*/
private int threshold;//阈值
/**
* The load factor for the hashtable.
*
* @serial
*/
private float loadFactor;//加载因子
/**
* The number of times this Hashtable has been structurally modified
* Structural modifications are those that change the number of entries in
* the Hashtable or otherwise modify its internal structure (e.g.,
* rehash). This field is used to make iterators on Collection-views of
* the Hashtable fail-fast. (See ConcurrentModificationException).
*/
private transient int modCount = 0;//fail-fast机制，记录改变的数目
/** use serialVersionUID from JDK 1.0.2 for interoperability */
private static final long serialVersionUID = 1421746759512286392L;
/**
* Constructs a new, empty hashtable with the specified initial
* capacity and the specified load factor.
*
* @param initialCapacity the initial capacity of the hashtable.
* @param loadFactor the load factor of the hashtable.
* @exception IllegalArgumentException if the initial capacity is less
* than zero, or if the load factor is nonpositive.
*/
//还有初始大小和加载因子的构造函数
public Hashtable(int initialCapacity, float loadFactor) {
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
if (loadFactor <= 0 || Float.isNaN(loadFactor))
throw new IllegalArgumentException("Illegal Load: "+loadFactor);
if (initialCapacity==0)
initialCapacity = 1;
this.loadFactor = loadFactor;
table = new Entryc3f2d894ed311a524f031af7191b9ddc[initialCapacity];
threshold = (int)Math.min(initialCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
}
/**
* Constructs a new, empty hashtable with the specified initial capacity
* and default load factor (0.75).
*
* @param initialCapacity the initial capacity of the hashtable.
* @exception IllegalArgumentException if the initial capacity is less
* than zero.
*/
//初始大小和默认的0.75加载因子的构造函数
public Hashtable(int initialCapacity) {
this(initialCapacity, 0.75f);
}
/**
* Constructs a new, empty hashtable with a default initial capacity (11)
* and load factor (0.75).
*/
//使用默认的构造函数
public Hashtable() {
this(11, 0.75f);
}
/**
* Constructs a new hashtable with the same mappings as the given
* Map. The hashtable is created with an initial capacity sufficient to
* hold the mappings in the given Map and a default load factor (0.75).
*
* @param t the map whose mappings are to be placed in this map.
* @throws NullPointerException if the specified map is null.
* @since 1.2
*/
public Hashtable(Map11df7d36ed146da2cbbceeacbc3a1d74 t) {
this(Math.max(2*t.size(), 11), 0.75f);
putAll(t);
}
/**
* Returns the number of keys in this hashtable.
*
* @return the number of keys in this hashtable.
*/
//Hashtable中entry大小
public synchronized int size() {
return count;
}
/**
* Tests if this hashtable maps no keys to values.
*
* @return ffbe95d20f3893062224282accb13e8ftrue1cd55414ff5abdfea5dd958e7e547fdd if this hashtable maps no keys to values;
* ffbe95d20f3893062224282accb13e8ffalse1cd55414ff5abdfea5dd958e7e547fdd otherwise.
*/
//判断是否为空
public synchronized boolean isEmpty() {
return count == 0;
}
/**
* Returns an enumeration of the keys in this hashtable.
*
* @return an enumeration of the keys in this hashtable.
* @see Enumeration
* @see #elements()
* @see #keySet()
* @see Map
*/
//key值的枚举
public synchronized Enumeration245c3adc26563b673f7297c0b3777639 keys() {
return this.245c3adc26563b673f7297c0b3777639getEnumeration(KEYS);
}
/**
* Returns an enumeration of the values in this hashtable.
* Use the Enumeration methods on the returned object to fetch the elements
* sequentially.
*
* @return an enumeration of the values in this hashtable.
* @see java.util.Enumeration
* @see #keys()
* @see #values()
* @see Map
*/
//value的枚举
public synchronized Enumerationd94943c0b4933ad8cac500132f64757f elements() {
return this.d94943c0b4933ad8cac500132f64757fgetEnumeration(VALUES);
}
/**
* Tests if some key maps into the specified value in this hashtable.
* This operation is more expensive than the {@link #containsKey
* containsKey} method.
*
* e388a4556c0f65e1904146cc1a846beeNote that this method is identical in functionality to
* {@link #containsValue containsValue}, (which is part of the
* {@link Map} interface in the collections framework).
*
* @param value a value to search for
* @return ffbe95d20f3893062224282accb13e8ftrue1cd55414ff5abdfea5dd958e7e547fdd if and only if some key maps to the
* ffbe95d20f3893062224282accb13e8fvalue1cd55414ff5abdfea5dd958e7e547fdd argument in this hashtable as
* determined by the 78f983dbc27872ba42409adefe5049d9equalsd98ca7951c814b9263d12f482df06c69 method;
* ffbe95d20f3893062224282accb13e8ffalse1cd55414ff5abdfea5dd958e7e547fdd otherwise.
* @exception NullPointerException if the value is ffbe95d20f3893062224282accb13e8fnull1cd55414ff5abdfea5dd958e7e547fdd
*/
//判断是否包含某个值
public synchronized boolean contains(Object value) {
if (value == null) {
throw new NullPointerException();
}
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
for (int i = tab.length ; i-- > 0 ;) {
for (Entryc3f2d894ed311a524f031af7191b9ddc e = tab[i] ; e != null ; e = e.next) {
if (e.value.equals(value)) {
return true;
}
}
}
return false;
}
/**
* Returns true if this hashtable maps one or more keys to this value.
*
* e388a4556c0f65e1904146cc1a846beeNote that this method is identical in functionality to {@link
* #contains contains} (which predates the {@link Map} interface).
*
* @param value value whose presence in this hashtable is to be tested
* @return 78f983dbc27872ba42409adefe5049d9trued98ca7951c814b9263d12f482df06c69 if this map maps one or more keys to the
* specified value
* @throws NullPointerException if the value is ffbe95d20f3893062224282accb13e8fnull1cd55414ff5abdfea5dd958e7e547fdd
* @since 1.2
*/
public boolean containsValue(Object value) {
return contains(value);
}
/**
* Tests if the specified object is a key in this hashtable.
*
* @param key possible key
* @return ffbe95d20f3893062224282accb13e8ftrue1cd55414ff5abdfea5dd958e7e547fdd if and only if the specified object
* is a key in this hashtable, as determined by the
* 78f983dbc27872ba42409adefe5049d9equalsd98ca7951c814b9263d12f482df06c69 method; ffbe95d20f3893062224282accb13e8ffalse1cd55414ff5abdfea5dd958e7e547fdd otherwise.
* @throws NullPointerException if the key is ffbe95d20f3893062224282accb13e8fnull1cd55414ff5abdfea5dd958e7e547fdd
* @see #contains(Object)
*/
//判断是否包含某个key
public synchronized boolean containsKey(Object key) {
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
for (Entryc3f2d894ed311a524f031af7191b9ddc e = tab[index] ; e != null ; e = e.next) {
if ((e.hash == hash) && e.key.equals(key)) {
return true;
}
}
return false;
}
/**
* Returns the value to which the specified key is mapped,
* or {@code null} if this map contains no mapping for the key.
*
* e388a4556c0f65e1904146cc1a846beeMore formally, if this map contains a mapping from a key
* {@code k} to a value {@code v} such that {@code (key.equals(k))},
* then this method returns {@code v}; otherwise it returns
* {@code null}. (There can be at most one such mapping.)
*
* @param key the key whose associated value is to be returned
* @return the value to which the specified key is mapped, or
* {@code null} if this map contains no mapping for the key
* @throws NullPointerException if the specified key is null
* @see #put(Object, Object)
*/
//获得某个key对应的value
@SuppressWarnings("unchecked")
public synchronized V get(Object key) {
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
for (Entryc3f2d894ed311a524f031af7191b9ddc e = tab[index] ; e != null ; e = e.next) {
if ((e.hash == hash) && e.key.equals(key)) {
return (V)e.value;
}
}
return null;
}
/**
* The maximum size of array to allocate.
* Some VMs reserve some header words in an array.
* Attempts to allocate larger arrays may result in
* OutOfMemoryError: Requested array size exceeds VM limit
*/
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/**
* Increases the capacity of and internally reorganizes this
* hashtable, in order to accommodate and access its entries more
* efficiently. This method is called automatically when the
* number of keys in the hashtable exceeds this hashtable's capacity
* and load factor.
*/
@SuppressWarnings("unchecked")
protected void rehash() {
int oldCapacity = table.length;
Entryc3f2d894ed311a524f031af7191b9ddc[] oldMap = table;
// overflow-conscious code
int newCapacity = (oldCapacity 5f877ca6e95c37537536a45618cbe95c 0) {
if (oldCapacity == MAX_ARRAY_SIZE)
// Keep running with MAX_ARRAY_SIZE buckets
return;
newCapacity = MAX_ARRAY_SIZE;
}
Entryc3f2d894ed311a524f031af7191b9ddc[] newMap = new Entryc3f2d894ed311a524f031af7191b9ddc[newCapacity];
modCount++;
threshold = (int)Math.min(newCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
table = newMap;
for (int i = oldCapacity ; i-- > 0 ;) {
for (Entryb77a8d9c3c319e50d4b02a976b347910 old = (Entryb77a8d9c3c319e50d4b02a976b347910)oldMap[i] ; old != null ; ) {
Entryb77a8d9c3c319e50d4b02a976b347910 e = old;
old = old.next;
int index = (e.hash & 0x7FFFFFFF) % newCapacity;
e.next = (Entryb77a8d9c3c319e50d4b02a976b347910)newMap[index];
newMap[index] = e;
}
}
}
private void addEntry(int hash, K key, V value, int index) {
modCount++;
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
if (count >= threshold) {
// Rehash the table if the threshold is exceeded
rehash();
tab = table;
hash = key.hashCode();
index = (hash & 0x7FFFFFFF) % tab.length;
}
// Creates the new entry.
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 e = (Entryb77a8d9c3c319e50d4b02a976b347910) tab[index];
tab[index] = new Entrya8093152e673feb7aba1828c43532094(hash, key, value, e);
count++;
}
/**
* Maps the specified ffbe95d20f3893062224282accb13e8fkey1cd55414ff5abdfea5dd958e7e547fdd to the specified
* ffbe95d20f3893062224282accb13e8fvalue1cd55414ff5abdfea5dd958e7e547fdd in this hashtable. Neither the key nor the
* value can be ffbe95d20f3893062224282accb13e8fnull1cd55414ff5abdfea5dd958e7e547fdd. e388a4556c0f65e1904146cc1a846bee
*
* The value can be retrieved by calling the ffbe95d20f3893062224282accb13e8fget1cd55414ff5abdfea5dd958e7e547fdd method
* with a key that is equal to the original key.
*
* @param key the hashtable key
* @param value the value
* @return the previous value of the specified key in this hashtable,
* or ffbe95d20f3893062224282accb13e8fnull1cd55414ff5abdfea5dd958e7e547fdd if it did not have one
* @exception NullPointerException if the key or value is
* ffbe95d20f3893062224282accb13e8fnull1cd55414ff5abdfea5dd958e7e547fdd
* @see Object#equals(Object)
* @see #get(Object)
*/
//key和value都不为空
public synchronized V put(K key, V value) {
// Make sure the value is not null
if (value == null) {
throw new NullPointerException();
}
// Makes sure the key is not already in the hashtable.
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 entry = (Entryb77a8d9c3c319e50d4b02a976b347910)tab[index];
for(; entry != null ; entry = entry.next) {
if ((entry.hash == hash) && entry.key.equals(key)) {
V old = entry.value;
entry.value = value;
return old;
}
}
addEntry(hash, key, value, index);
return null;
}
/**
* Removes the key (and its corresponding value) from this
* hashtable. This method does nothing if the key is not in the hashtable.
*
* @param key the key that needs to be removed
* @return the value to which the key had been mapped in this hashtable,
* or ffbe95d20f3893062224282accb13e8fnull1cd55414ff5abdfea5dd958e7e547fdd if the key did not have a mapping
* @throws NullPointerException if the key is ffbe95d20f3893062224282accb13e8fnull1cd55414ff5abdfea5dd958e7e547fdd
*/
//删除某个key对应的value
public synchronized V remove(Object key) {
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 e = (Entryb77a8d9c3c319e50d4b02a976b347910)tab[index];
for(Entryb77a8d9c3c319e50d4b02a976b347910 prev = null ; e != null ; prev = e, e = e.next) {
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;
}
/**
* Copies all of the mappings from the specified map to this hashtable.
* These mappings will replace any mappings that this hashtable had for any
* of the keys currently in the specified map.
*
* @param t mappings to be stored in this map
* @throws NullPointerException if the specified map is null
* @since 1.2
*/
public synchronized void putAll(Map11df7d36ed146da2cbbceeacbc3a1d74 t) {
for (Map.Entry11df7d36ed146da2cbbceeacbc3a1d74 e : t.entrySet())
put(e.getKey(), e.getValue());
}
/**
* Clears this hashtable so that it contains no keys.
*/
//清空
public synchronized void clear() {
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
modCount++;
for (int index = tab.length; --index >= 0; )
tab[index] = null;
count = 0;
}
/**
* Creates a shallow copy of this hashtable. All the structure of the
* hashtable itself is copied, but the keys and values are not cloned.
* This is a relatively expensive operation.
*
* @return a clone of the hashtable
*/
//浅拷贝
public synchronized Object clone() {
try {
Hashtablec3f2d894ed311a524f031af7191b9ddc t = (Hashtablec3f2d894ed311a524f031af7191b9ddc)super.clone();
t.table = new Entryc3f2d894ed311a524f031af7191b9ddc[table.length];
for (int i = table.length ; i-- > 0 ; ) {
t.table[i] = (table[i] != null)
? (Entryc3f2d894ed311a524f031af7191b9ddc) 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 Cloneable
throw new InternalError(e);
}
}
/**
* Returns a string representation of this 78f983dbc27872ba42409adefe5049d9Hashtabled98ca7951c814b9263d12f482df06c69 object
* in the form of a set of entries, enclosed in braces and separated
* by the ASCII characters "78f983dbc27872ba42409adefe5049d9, d98ca7951c814b9263d12f482df06c69" (comma and space). Each
* entry is rendered as the key, an equals sign 78f983dbc27872ba42409adefe5049d9=d98ca7951c814b9263d12f482df06c69, and the
* associated element, where the 78f983dbc27872ba42409adefe5049d9toStringd98ca7951c814b9263d12f482df06c69 method is used to
* convert the key and element to strings.
*
* @return a string representation of this hashtable
*/
public synchronized String toString() {
int max = size() - 1;
if (max == -1)
return "{}";
StringBuilder sb = new StringBuilder();
Iterator<Map.Entryb77a8d9c3c319e50d4b02a976b347910> it = entrySet().iterator();
sb.append('{');
for (int i = 0; ; i++) {
Map.Entryb77a8d9c3c319e50d4b02a976b347910 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(", ");
}
}
private 8742468051c85b06f0a0af9e3e506b5c Enumeration8742468051c85b06f0a0af9e3e506b5c getEnumeration(int type) {
if (count == 0) {
return Collections.emptyEnumeration();
} else {
return new Enumeratora8093152e673feb7aba1828c43532094(type, false);
}
}
private 8742468051c85b06f0a0af9e3e506b5c Iterator8742468051c85b06f0a0af9e3e506b5c getIterator(int type) {
if (count == 0) {
return Collections.emptyIterator();
} else {
return new Enumeratora8093152e673feb7aba1828c43532094(type, true);
}
}
// Views
/**
* Each of these fields are initialized to contain an instance of the
* appropriate view the first time this view is requested. The views are
* stateless, so there's no reason to create more than one of each.
*/
private transient volatile Set245c3adc26563b673f7297c0b3777639 keySet;
private transient volatile Set<Map.Entryb77a8d9c3c319e50d4b02a976b347910> entrySet;
private transient volatile Collectiond94943c0b4933ad8cac500132f64757f values;
/**
* Returns a {@link Set} view of the keys contained in this map.
* The set is backed by the map, so changes to the map are
* reflected in the set, and vice-versa. If the map is modified
* while an iteration over the set is in progress (except through
* the iterator's own 78f983dbc27872ba42409adefe5049d9removed98ca7951c814b9263d12f482df06c69 operation), the results of
* the iteration are undefined. The set supports element removal,
* which removes the corresponding mapping from the map, via the
* 78f983dbc27872ba42409adefe5049d9Iterator.removed98ca7951c814b9263d12f482df06c69, 78f983dbc27872ba42409adefe5049d9Set.removed98ca7951c814b9263d12f482df06c69,
* 78f983dbc27872ba42409adefe5049d9removeAlld98ca7951c814b9263d12f482df06c69, 78f983dbc27872ba42409adefe5049d9retainAlld98ca7951c814b9263d12f482df06c69, and 78f983dbc27872ba42409adefe5049d9cleard98ca7951c814b9263d12f482df06c69
* operations. It does not support the 78f983dbc27872ba42409adefe5049d9addd98ca7951c814b9263d12f482df06c69 or 78f983dbc27872ba42409adefe5049d9addAlld98ca7951c814b9263d12f482df06c69
* operations.
*
* @since 1.2
*/
public Set245c3adc26563b673f7297c0b3777639 keySet() {
if (keySet == null)
keySet = Collections.synchronizedSet(new KeySet(), this);
return keySet;
}
private class KeySet extends AbstractSet245c3adc26563b673f7297c0b3777639 {
public Iterator245c3adc26563b673f7297c0b3777639 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();
}
}
/**
* Returns a {@link Set} view of the mappings contained in this map.
* The set is backed by the map, so changes to the map are
* reflected in the set, and vice-versa. If the map is modified
* while an iteration over the set is in progress (except through
* the iterator's own 78f983dbc27872ba42409adefe5049d9removed98ca7951c814b9263d12f482df06c69 operation, or through the
* 78f983dbc27872ba42409adefe5049d9setValued98ca7951c814b9263d12f482df06c69 operation on a map entry returned by the
* iterator) the results of the iteration are undefined. The set
* supports element removal, which removes the corresponding
* mapping from the map, via the 78f983dbc27872ba42409adefe5049d9Iterator.removed98ca7951c814b9263d12f482df06c69,
* 78f983dbc27872ba42409adefe5049d9Set.removed98ca7951c814b9263d12f482df06c69, 78f983dbc27872ba42409adefe5049d9removeAlld98ca7951c814b9263d12f482df06c69, 78f983dbc27872ba42409adefe5049d9retainAlld98ca7951c814b9263d12f482df06c69 and
* 78f983dbc27872ba42409adefe5049d9cleard98ca7951c814b9263d12f482df06c69 operations. It does not support the
* 78f983dbc27872ba42409adefe5049d9addd98ca7951c814b9263d12f482df06c69 or 78f983dbc27872ba42409adefe5049d9addAlld98ca7951c814b9263d12f482df06c69 operations.
*
* @since 1.2
*/
public Set<Map.Entryb77a8d9c3c319e50d4b02a976b347910> entrySet() {
if (entrySet==null)
entrySet = Collections.synchronizedSet(new EntrySet(), this);
return entrySet;
}
private class EntrySet extends AbstractSet<Map.Entryb77a8d9c3c319e50d4b02a976b347910> {
public Iterator<Map.Entryb77a8d9c3c319e50d4b02a976b347910> iterator() {
return getIterator(ENTRIES);
}
public boolean add(Map.Entryb77a8d9c3c319e50d4b02a976b347910 o) {
return super.add(o);
}
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entryc3f2d894ed311a524f031af7191b9ddc entry = (Map.Entryc3f2d894ed311a524f031af7191b9ddc)o;
Object key = entry.getKey();
Entryc3f2d894ed311a524f031af7191b9ddc[] tab = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
for (Entryc3f2d894ed311a524f031af7191b9ddc e = tab[index]; e != null; e = e.next)
if (e.hash==hash && e.equals(entry))
return true;
return false;
}
public boolean remove(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entryc3f2d894ed311a524f031af7191b9ddc entry = (Map.Entryc3f2d894ed311a524f031af7191b9ddc) o;
Object key = entry.getKey();
Entryc3f2d894ed311a524f031af7191b9ddc[] tab = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 e = (Entryb77a8d9c3c319e50d4b02a976b347910)tab[index];
for(Entryb77a8d9c3c319e50d4b02a976b347910 prev = null; e != null; prev = e, e = e.next) {
if (e.hash==hash && e.equals(entry)) {
modCount++;
if (prev != null)
prev.next = e.next;
else
tab[index] = e.next;
count--;
e.value = null;
return true;
}
}
return false;
}
public int size() {
return count;
}
public void clear() {
Hashtable.this.clear();
}
}
/**
* Returns a {@link Collection} view of the values contained in this map.
* The collection is backed by the map, so changes to the map are
* reflected in the collection, and vice-versa. If the map is
* modified while an iteration over the collection is in progress
* (except through the iterator's own 78f983dbc27872ba42409adefe5049d9removed98ca7951c814b9263d12f482df06c69 operation),
* the results of the iteration are undefined. The collection
* supports element removal, which removes the corresponding
* mapping from the map, via the 78f983dbc27872ba42409adefe5049d9Iterator.removed98ca7951c814b9263d12f482df06c69,
* 78f983dbc27872ba42409adefe5049d9Collection.removed98ca7951c814b9263d12f482df06c69, 78f983dbc27872ba42409adefe5049d9removeAlld98ca7951c814b9263d12f482df06c69,
* 78f983dbc27872ba42409adefe5049d9retainAlld98ca7951c814b9263d12f482df06c69 and 78f983dbc27872ba42409adefe5049d9cleard98ca7951c814b9263d12f482df06c69 operations. It does not
* support the 78f983dbc27872ba42409adefe5049d9addd98ca7951c814b9263d12f482df06c69 or 78f983dbc27872ba42409adefe5049d9addAlld98ca7951c814b9263d12f482df06c69 operations.
*
* @since 1.2
*/
public Collectiond94943c0b4933ad8cac500132f64757f values() {
if (values==null)
values = Collections.synchronizedCollection(new ValueCollection(),
this);
return values;
}
private class ValueCollection extends AbstractCollectiond94943c0b4933ad8cac500132f64757f {
public Iteratord94943c0b4933ad8cac500132f64757f 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
/**
* Compares the specified Object with this Map for equality,
* as per the definition in the Map interface.
*
* @param o object to be compared for equality with this hashtable
* @return true if the specified Object is equal to this Map
* @see Map#equals(Object)
* @since 1.2
*/
public synchronized boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Map))
return false;
Mapc3f2d894ed311a524f031af7191b9ddc t = (Mapc3f2d894ed311a524f031af7191b9ddc) o;
if (t.size() != size())
return false;
try {
Iterator<Map.Entryb77a8d9c3c319e50d4b02a976b347910> i = entrySet().iterator();
while (i.hasNext()) {
Map.Entryb77a8d9c3c319e50d4b02a976b347910 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;
}
/**
* Returns the hash code value for this Map as per the definition in the
* Map interface.
*
* @see Map#hashCode()
* @since 1.2
*/
public synchronized int hashCode() {
/*
* This code detects the recursion caused by computing the hash code
* of a self-referential hash table and prevents the stack overflow
* that would otherwise result. This allows certain 1.1-era
* applets with self-referential hash tables to work. This code
* abuses the loadFactor field to do double-duty as a hashCode
* in progress flag, so as not to worsen the space performance.
* A negative load factor indicates that hash code computation is
* in progress.
*/
int h = 0;
if (count == 0 || loadFactor < 0)
return h; // Returns zero
loadFactor = -loadFactor; // Mark hashCode computation in progress
Entryc3f2d894ed311a524f031af7191b9ddc[] tab = table;
for (Entryc3f2d894ed311a524f031af7191b9ddc entry : tab) {
while (entry != null) {
h += entry.hashCode();
entry = entry.next;
}
}
loadFactor = -loadFactor; // Mark hashCode computation complete
return h;
}
@Override
public synchronized V getOrDefault(Object key, V defaultValue) {
V result = get(key);
return (null == result) ? defaultValue : result;
}
@SuppressWarnings("unchecked")
@Override
public synchronized void forEach(BiConsumer8d7aa65c8046027ea338ee53f830d46e action) {
Objects.requireNonNull(action); // explicit check required in case
// table is empty.
final int expectedModCount = modCount;
Entryd43304c59d62d300b67a59666cfd3cea[] tab = table;
for (Entryd43304c59d62d300b67a59666cfd3cea entry : tab) {
while (entry != null) {
action.accept((K)entry.key, (V)entry.value);
entry = entry.next;
if (expectedModCount != modCount) {
throw new ConcurrentModificationException();
}
}
}
}
@SuppressWarnings("unchecked")
@Override
public synchronized void replaceAll(BiFunction0a1b16d994d218d93e3e331534b14776 function) {
Objects.requireNonNull(function); // explicit check required in case
// table is empty.
final int expectedModCount = modCount;
Entry81079595401ce1162abe0d5a660013d8[] tab = (Entry81079595401ce1162abe0d5a660013d8[])table;
for (Entry81079595401ce1162abe0d5a660013d8 entry : tab) {
while (entry != null) {
entry.value = Objects.requireNonNull(
function.apply(entry.key, entry.value));
entry = entry.next;
if (expectedModCount != modCount) {
throw new ConcurrentModificationException();
}
}
}
}
@Override
public synchronized V putIfAbsent(K key, V value) {
Objects.requireNonNull(value);
// Makes sure the key is not already in the hashtable.
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 entry = (Entryb77a8d9c3c319e50d4b02a976b347910)tab[index];
for (; entry != null; entry = entry.next) {
if ((entry.hash == hash) && entry.key.equals(key)) {
V old = entry.value;
if (old == null) {
entry.value = value;
}
return old;
}
}
addEntry(hash, key, value, index);
return null;
}
@Override
public synchronized boolean remove(Object key, Object value) {
Objects.requireNonNull(value);
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 e = (Entryb77a8d9c3c319e50d4b02a976b347910)tab[index];
for (Entryb77a8d9c3c319e50d4b02a976b347910 prev = null; e != null; prev = e, e = e.next) {
if ((e.hash == hash) && e.key.equals(key) && e.value.equals(value)) {
modCount++;
if (prev != null) {
prev.next = e.next;
} else {
tab[index] = e.next;
}
count--;
e.value = null;
return true;
}
}
return false;
}
@Override
public synchronized boolean replace(K key, V oldValue, V newValue) {
Objects.requireNonNull(oldValue);
Objects.requireNonNull(newValue);
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 e = (Entryb77a8d9c3c319e50d4b02a976b347910)tab[index];
for (; e != null; e = e.next) {
if ((e.hash == hash) && e.key.equals(key)) {
if (e.value.equals(oldValue)) {
e.value = newValue;
return true;
} else {
return false;
}
}
}
return false;
}
@Override
public synchronized V replace(K key, V value) {
Objects.requireNonNull(value);
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 e = (Entryb77a8d9c3c319e50d4b02a976b347910)tab[index];
for (; e != null; e = e.next) {
if ((e.hash == hash) && e.key.equals(key)) {
V oldValue = e.value;
e.value = value;
return oldValue;
}
}
return null;
}
@Override
public synchronized V computeIfAbsent(K key, Functionb68c911977e56dedeb85de82f5d80518 mappingFunction) {
Objects.requireNonNull(mappingFunction);
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 e = (Entryb77a8d9c3c319e50d4b02a976b347910)tab[index];
for (; e != null; e = e.next) {
if (e.hash == hash && e.key.equals(key)) {
// Hashtable not accept null value
return e.value;
}
}
V newValue = mappingFunction.apply(key);
if (newValue != null) {
addEntry(hash, key, newValue, index);
}
return newValue;
}
@Override
public synchronized V computeIfPresent(K key, BiFunction0a1b16d994d218d93e3e331534b14776 remappingFunction) {
Objects.requireNonNull(remappingFunction);
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 e = (Entryb77a8d9c3c319e50d4b02a976b347910)tab[index];
for (Entryb77a8d9c3c319e50d4b02a976b347910 prev = null; e != null; prev = e, e = e.next) {
if (e.hash == hash && e.key.equals(key)) {
V newValue = remappingFunction.apply(key, e.value);
if (newValue == null) {
modCount++;
if (prev != null) {
prev.next = e.next;
} else {
tab[index] = e.next;
}
count--;
} else {
e.value = newValue;
}
return newValue;
}
}
return null;
}
@Override
public synchronized V compute(K key, BiFunction0a1b16d994d218d93e3e331534b14776 remappingFunction) {
Objects.requireNonNull(remappingFunction);
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 e = (Entryb77a8d9c3c319e50d4b02a976b347910)tab[index];
for (Entryb77a8d9c3c319e50d4b02a976b347910 prev = null; e != null; prev = e, e = e.next) {
if (e.hash == hash && Objects.equals(e.key, key)) {
V newValue = remappingFunction.apply(key, e.value);
if (newValue == null) {
modCount++;
if (prev != null) {
prev.next = e.next;
} else {
tab[index] = e.next;
}
count--;
} else {
e.value = newValue;
}
return newValue;
}
}
V newValue = remappingFunction.apply(key, null);
if (newValue != null) {
addEntry(hash, key, newValue, index);
}
return newValue;
}
@Override
public synchronized V merge(K key, V value, BiFunctiona9451a6954651d01dcb928f097d6d988 remappingFunction) {
Objects.requireNonNull(remappingFunction);
Entryc3f2d894ed311a524f031af7191b9ddc tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 e = (Entryb77a8d9c3c319e50d4b02a976b347910)tab[index];
for (Entryb77a8d9c3c319e50d4b02a976b347910 prev = null; e != null; prev = e, e = e.next) {
if (e.hash == hash && e.key.equals(key)) {
V newValue = remappingFunction.apply(e.value, value);
if (newValue == null) {
modCount++;
if (prev != null) {
prev.next = e.next;
} else {
tab[index] = e.next;
}
count--;
} else {
e.value = newValue;
}
return newValue;
}
}
if (value != null) {
addEntry(hash, key, value, index);
}
return value;
}
/**
* Save the state of the Hashtable to a stream (i.e., serialize it).
*
* @serialData The 5a8028ccc7a7e27417bff9f05adf5932capacity72ac96585ae54b6ae11f849d2649d9e6 of the Hashtable (the length of the
* bucket array) is emitted (int), followed by the
* 5a8028ccc7a7e27417bff9f05adf5932size72ac96585ae54b6ae11f849d2649d9e6 of the Hashtable (the number of key-value
* mappings), followed by the key (Object) and value (Object)
* for each key-value mapping represented by the Hashtable
* The key-value mappings are emitted in no particular order.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws IOException {
Entry9c529c9823c5e43e5785844691736ac0 entryStack = null;
synchronized (this) {
// Write out the length, threshold, loadfactor
s.defaultWriteObject();
// Write out length, count of elements
s.writeInt(table.length);
s.writeInt(count);
// Stack copies of the entries in the table
for (int index = 0; index < table.length; index++) {
Entryc3f2d894ed311a524f031af7191b9ddc entry = table[index];
while (entry != null) {
entryStack =
new Entrya8093152e673feb7aba1828c43532094(0, entry.key, entry.value, entryStack);
entry = entry.next;
}
}
}
// Write out the key/value objects from the stacked entries
while (entryStack != null) {
s.writeObject(entryStack.key);
s.writeObject(entryStack.value);
entryStack = entryStack.next;
}
}
/**
* Reconstitute the Hashtable from a stream (i.e., deserialize it).
*/
private void readObject(java.io.ObjectInputStream s)
throws IOException, ClassNotFoundException
{
// Read in the length, threshold, and loadfactor
s.defaultReadObject();
// Read the original length of the array and number of elements
int origlength = s.readInt();
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;
table = new Entryc3f2d894ed311a524f031af7191b9ddc[length];
threshold = (int)Math.min(length * loadFactor, MAX_ARRAY_SIZE + 1);
count = 0;
// Read the number of elements and then all the key/value objects
for (; elements > 0; elements--) {
@SuppressWarnings("unchecked")
K key = (K)s.readObject();
@SuppressWarnings("unchecked")
V value = (V)s.readObject();
// synch could be eliminated for performance
reconstitutionPut(table, key, value);
}
}
/**
* The put method used by readObject. This is provided because put
* is overridable and should not be called in readObject since the
* subclass will not yet be initialized.
*
* e388a4556c0f65e1904146cc1a846beeThis differs from the regular put method in several ways. No
* checking for rehashing is necessary since the number of elements
* initially in the table is known. The modCount is not incremented
* because we are creating a new instance. Also, no return value
* is needed.
*/
private void reconstitutionPut(Entryc3f2d894ed311a524f031af7191b9ddc[] 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 (Entryc3f2d894ed311a524f031af7191b9ddc 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.
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 e = (Entryb77a8d9c3c319e50d4b02a976b347910)tab[index];
tab[index] = new Entrya8093152e673feb7aba1828c43532094(hash, key, value, e);
count++;
}
/**
* Hashtable bucket collision list entry
*/
private static class Entryb77a8d9c3c319e50d4b02a976b347910 implements Map.Entryb77a8d9c3c319e50d4b02a976b347910 {
final int hash;
final K key;
V value;
Entryb77a8d9c3c319e50d4b02a976b347910 next;
protected Entry(int hash, K key, V value, Entryb77a8d9c3c319e50d4b02a976b347910 next) {
this.hash = hash;
this.key = key;
this.value = value;
this.next = next;
}
@SuppressWarnings("unchecked")
protected Object clone() {
return new Entrya8093152e673feb7aba1828c43532094(hash, key, value,
(next==null ? null : (Entryb77a8d9c3c319e50d4b02a976b347910) next.clone()));
}
// Map.Entry Ops
public K getKey() {
return key;
}
public V getValue() {
return value;
}
public V setValue(V value) {
if (value == null)
throw new NullPointerException();
V oldValue = this.value;
this.value = value;
return oldValue;
}
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entryc3f2d894ed311a524f031af7191b9ddc e = (Map.Entryc3f2d894ed311a524f031af7191b9ddc)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 ^ Objects.hashCode(value);
}
public String toString() {
return key.toString()+"="+value.toString();
}
}
// Types of Enumerations/Iterations
private static final int KEYS = 0;
private static final int VALUES = 1;
private static final int ENTRIES = 2;
/**
* A hashtable enumerator class. This class implements both the
* Enumeration and Iterator interfaces, but inpidual instances
* can be created with the Iterator methods disabled. This is necessary
* to avoid unintentionally increasing the capabilities granted a user
* by passing an Enumeration.
*/
private class Enumerator8742468051c85b06f0a0af9e3e506b5c implements Enumeration8742468051c85b06f0a0af9e3e506b5c, Iterator8742468051c85b06f0a0af9e3e506b5c {
Entryc3f2d894ed311a524f031af7191b9ddc[] table = Hashtable.this.table;
int index = table.length;
Entryc3f2d894ed311a524f031af7191b9ddc entry;
Entryc3f2d894ed311a524f031af7191b9ddc lastReturned;
int type;
/**
* Indicates whether this Enumerator is serving as an Iterator
* or an Enumeration. (true -> Iterator).
*/
boolean iterator;
/**
* The modCount value that the iterator believes that the backing
* Hashtable should have. If this expectation is violated, the iterator
* has detected concurrent modification.
*/
protected int expectedModCount = modCount;
Enumerator(int type, boolean iterator) {
this.type = type;
this.iterator = iterator;
}
public boolean hasMoreElements() {
Entryc3f2d894ed311a524f031af7191b9ddc e = entry;
int i = index;
Entryc3f2d894ed311a524f031af7191b9ddc[] t = table;
/* Use locals for faster loop iteration */
while (e == null && i > 0) {
e = t[--i];
}
entry = e;
index = i;
return e != null;
}
@SuppressWarnings("unchecked")
public T nextElement() {
Entryc3f2d894ed311a524f031af7191b9ddc et = entry;
int i = index;
Entryc3f2d894ed311a524f031af7191b9ddc[] t = table;
/* Use locals for faster loop iteration */
while (et == null && i > 0) {
et = t[--i];
}
entry = et;
index = i;
if (et != null) {
Entryc3f2d894ed311a524f031af7191b9ddc e = lastReturned = entry;
entry = e.next;
return type == KEYS ? (T)e.key : (type == VALUES ? (T)e.value : (T)e);
}
throw new NoSuchElementException("Hashtable Enumerator");
}
// Iterator methods
public boolean hasNext() {
return hasMoreElements();
}
public T next() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
return nextElement();
}
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) {
Entryc3f2d894ed311a524f031af7191b9ddc[] tab = Hashtable.this.table;
int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length;
@SuppressWarnings("unchecked")
Entryb77a8d9c3c319e50d4b02a976b347910 e = (Entryb77a8d9c3c319e50d4b02a976b347910)tab[index];
for(Entryb77a8d9c3c319e50d4b02a976b347910 prev = null; e != null; prev = e, e = e.next) {
if (e == lastReturned) {
modCount++;
expectedModCount++;
if (prev == null)
tab[index] = e.next;
else
prev.next = e.next;
count--;
lastReturned = null;
return;
}
}
throw new ConcurrentModificationException();
}
}
}
}以上是Java集合之詳細介紹Hashtable（圖文）的詳細內容。更多資訊請關注PHP中文網其他相關文章！
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