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java.lang.Objectcom.jaxfront.core.util.DoubleKeyHashtable
com.jaxfront.core.util.DoubleKeyHashtableUnsynced
public class DoubleKeyHashtableUnsynced
This class implements a hashtable, which maps keys to values. Any non-null
object can be used as a key or as a value.
To successfully store and retrieve objects from a hashtable, the objects used
as keys must implement the hashCode
method and the
equals
method.
An instance of DoubleKeyHashtable
has two parameters that
affect its performance: initial capacity and load factor. The
capacity is the number of buckets in the hash table, and the
initial capacity is simply the capacity at the time the hash table is
created. Note that the hash table is open: in the case of a "hash
collision", a single bucket stores multiple entries, which must be searched
sequentially. The load factor is a measure of how full the hash table
is allowed to get before its capacity is automatically increased. When the
number of entries in the hashtable exceeds the product of the load factor and
the current capacity, the capacity is increased by calling the
rehash
method.
Generally, the default load factor (.75) offers a good tradeoff between time and space costs. Higher values decrease the space overhead but increase the time cost to look up an entry (which is reflected in most DoubleKeyHashtable operations, including get and put).
The initial capacity controls a tradeoff between wasted space and the need
for rehash
operations, which are time-consuming. No
rehash
operations will ever occur if the initial
capacity is greater than the maximum number of entries the
DoubleKeyHashtable will contain divided by its load factor.
However, setting the initial capacity too high can waste space.
If many entries are to be made into a DoubleKeyHashtable
,
creating it with a sufficiently large capacity may allow the entries to be
inserted more efficiently than letting it perform automatic rehashing as
needed to grow the table.
This example creates a hashtable of numbers. It uses the names of the numbers as keys:
DoubleKeyHashtable numbers = new DoubleKeyHashtable(); numbers.put("one", new Integer(1)); numbers.put("two", new Integer(2)); numbers.put("three", new Integer(3));
To retrieve a number, use the following code:
Integer n = (Integer) numbers.get("two"); if (n != null) { System.out.println("two = " + n); }
As of the Java 2 platform v1.2, this class has been retrofitted to implement Map, so that it becomes a part of Java's collection framework. Unlike the new collection implementations, DoubleKeyHashtable is synchronized.
The Iterators returned by the iterator and listIterator methods of the Collections returned by all of DoubleKeyHashtable's "collection view methods" are fail-fast: if the DoubleKeyHashtable is structurally modified at any time after the Iterator is created, in any way except through the Iterator's own remove or add methods, the Iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the Iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future. The Enumerations returned by DoubleKeyHashtable's keys and values methods are not fail-fast.
Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.
This class is a member of the Java Collections Framework.
Object.equals(java.lang.Object)
,
Object.hashCode()
,
rehash()
,
Collection
,
Map
,
HashMap
,
TreeMap
,
Serialized FormNested Class Summary |
---|
Nested classes/interfaces inherited from class com.jaxfront.core.util.DoubleKeyHashtable |
---|
DoubleKeyHashtable.Entry |
Constructor Summary | |
---|---|
DoubleKeyHashtableUnsynced()
Constructs a new, empty hashtable with a default initial capacity (11) and load factor, which is 0.75. |
|
DoubleKeyHashtableUnsynced(int initialCapacity)
Constructs a new, empty hashtable with the specified initial capacity and default load factor, which is 0.75. |
|
DoubleKeyHashtableUnsynced(int initialCapacity,
float loadFactor)
Constructs a new, empty hashtable with the specified initial capacity and the specified load factor. |
Method Summary | |
---|---|
void |
clear()
Clears this hashtable so that it contains no keys. |
java.lang.Object |
clone()
Creates a shallow copy of this hashtable. |
boolean |
contains(java.lang.Object value)
Tests if some key maps into the specified value in this hashtable. |
boolean |
containsKey(java.lang.Object key1,
java.lang.Object key2)
Tests if the specified object is a key in this hashtable. |
boolean |
containsValue(java.lang.Object value)
Returns true if this DoubleKeyHashtable maps one or more keys to this value. |
java.lang.String |
createTestStringKey(java.lang.String a,
java.lang.String b)
|
java.util.Enumeration |
elements()
Returns an enumeration of the values in this hashtable. |
java.util.Set |
entrySet()
Returns a Set view of the entries contained in this DoubleKeyHashtable. |
boolean |
equals(java.lang.Object o)
Compares the specified Object with this Map for equality, as per the definition in the Map interface. |
java.lang.Object |
get(DoubleKeyHashtable.Entry keyEntry)
|
java.lang.Object |
get(java.lang.Object key,
java.lang.Object key2)
Returns the value to which the specified key is mapped in this hashtable. |
int |
hashCode()
Returns the hash code value for this Map as per the definition in the Map interface. |
boolean |
isEmpty()
Tests if this hashtable maps no keys to values. |
java.util.Enumeration |
keys()
Returns an enumeration of the keys in this hashtable. |
java.util.Set |
keySet()
Returns a Set view of the keys contained in this DoubleKeyHashtable. |
static void |
main(java.lang.String[] args)
|
java.lang.Object |
put(java.lang.Object key1,
java.lang.Object key2,
java.lang.Object value)
Maps the specified key to the specified value
in this hashtable. |
java.lang.Object |
remove(DoubleKeyHashtable.Entry aEntry)
|
java.lang.Object |
remove(java.lang.Object key1,
java.lang.Object key2)
Removes the key (and its corresponding value) from this hashtable. |
int |
removePrimary(java.lang.Object key)
|
int |
removeSecondary(java.lang.Object key)
|
java.lang.Object |
removeValue(java.lang.Object value)
|
int |
size()
Returns the number of keys in this hashtable. |
void |
test()
|
java.lang.String |
toString()
Returns a string representation of this DoubleKeyHashtable object in the form of a set of entries, enclosed in braces and separated by the ASCII characters ", " (comma and space). |
java.util.Collection |
values()
Returns a Collection view of the values contained in this DoubleKeyHashtable. |
Methods inherited from class java.lang.Object |
---|
getClass, notify, notifyAll, wait, wait, wait |
Constructor Detail |
---|
public DoubleKeyHashtableUnsynced(int initialCapacity, float loadFactor)
initialCapacity
- the initial capacity of the hashtable.loadFactor
- the load factor of the hashtable.
java.lang.IllegalArgumentException
- if the initial capacity is less than zero, or if the load
factor is nonpositive.public DoubleKeyHashtableUnsynced(int initialCapacity)
initialCapacity
- the initial capacity of the hashtable.
java.lang.IllegalArgumentException
- if the initial capacity is less than zero.public DoubleKeyHashtableUnsynced()
Method Detail |
---|
public int size()
size
in class DoubleKeyHashtable
public boolean isEmpty()
isEmpty
in class DoubleKeyHashtable
true
if this hashtable maps no keys to values;
false
otherwise.public java.util.Enumeration keys()
keys
in class DoubleKeyHashtable
Enumeration
,
elements()
,
keySet()
,
Map
public java.util.Enumeration elements()
elements
in class DoubleKeyHashtable
Enumeration
,
keys()
,
values()
,
Map
public boolean contains(java.lang.Object value)
containsKey
method.
Note that this method is identical in functionality to containsValue, (which is part of the Map interface in the collections framework).
contains
in class DoubleKeyHashtable
value
- a value to search for.
true
if and only if some key maps to the
value
argument in this hashtable as determined by
the equals method; false
otherwise.
java.lang.NullPointerException
- if the value is null
.#containsKey(Object)
,
containsValue(Object)
,
Map
public boolean containsValue(java.lang.Object value)
Note that this method is identical in functionality to contains (which predates the Map interface).
containsValue
in class DoubleKeyHashtable
value
- value whose presence in this DoubleKeyHashtable is to be
tested.
java.lang.NullPointerException
- if the value is null
.Map
public boolean containsKey(java.lang.Object key1, java.lang.Object key2)
containsKey
in class DoubleKeyHashtable
key
- possible key.
true
if and only if the specified object is a key
in this hashtable, as determined by the equals method;
false
otherwise.
java.lang.NullPointerException
- if the key is null
.contains(Object)
public java.lang.Object get(java.lang.Object key, java.lang.Object key2)
get
in class DoubleKeyHashtable
key
- a key in the hashtable.
null
if the key is not mapped to any value in this
hashtable.
java.lang.NullPointerException
- if the key is null
.#put(Object, Object)
public java.lang.Object get(DoubleKeyHashtable.Entry keyEntry)
get
in class DoubleKeyHashtable
public java.lang.Object put(java.lang.Object key1, java.lang.Object key2, java.lang.Object value)
key
to the specified value
in this hashtable. Neither the key nor the value can be null
.
The value can be retrieved by calling the get
method with
a key that is equal to the original key.
put
in class DoubleKeyHashtable
key
- the hashtable key.value
- the value.
null
if it did not have one.
java.lang.NullPointerException
- if the key or value is null
.Object.equals(Object)
,
#get(Object)
public java.lang.Object removeValue(java.lang.Object value)
removeValue
in class DoubleKeyHashtable
public java.lang.Object remove(java.lang.Object key1, java.lang.Object key2)
remove
in class DoubleKeyHashtable
key
- the key that needs to be removed.
null
if the key did not have a mapping.
java.lang.NullPointerException
- if the key is null
.public java.lang.Object remove(DoubleKeyHashtable.Entry aEntry)
remove
in class DoubleKeyHashtable
public int removePrimary(java.lang.Object key)
removePrimary
in class DoubleKeyHashtable
public int removeSecondary(java.lang.Object key)
removeSecondary
in class DoubleKeyHashtable
public void clear()
clear
in class DoubleKeyHashtable
public java.lang.Object clone()
clone
in class DoubleKeyHashtable
public java.lang.String toString()
Overrides to toString method of Object.
toString
in class DoubleKeyHashtable
public java.util.Set keySet()
keySet
in class DoubleKeyHashtable
public java.util.Set entrySet()
entrySet
in class DoubleKeyHashtable
Map.Entry
public java.util.Collection values()
values
in class DoubleKeyHashtable
public boolean equals(java.lang.Object o)
equals
in class DoubleKeyHashtable
o
- object to be compared for equality with this
DoubleKeyHashtable
Map.equals(Object)
public int hashCode()
hashCode
in class DoubleKeyHashtable
Map.hashCode()
public void test()
test
in class DoubleKeyHashtable
public java.lang.String createTestStringKey(java.lang.String a, java.lang.String b)
createTestStringKey
in class DoubleKeyHashtable
public static void main(java.lang.String[] args)
|
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