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java.lang.Object | +--waba.util.Hashtable
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 be String, because currently on SuperWaba only string objects implements hashCode method.
An instance of Hashtable
has two parameters that
affect its efficiency: its capacity and its load
factor. The load factor should be between 0.0 and 1.0. 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. Larger load factors use
memory more efficiently, at the expense of larger expected time
per lookup.
If many entries are to be made into a Hashtable
,
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:
Hashtable numbers = new Hashtable(); numbers.put("one", Convert.toString(1)); numbers.put("two", Convert.toString(2)); numbers.put("three", Convert.toString(3));
To retrieve a number, use the following code:
Important notes (added by guich)String n = (String)numbers.get("two"); if (n != null) { System.out.println("two = " + Convert.toInt(n)); }
There are no default constructor to decrease memory usage. Also,
thanks to Arthur van Hoff
Constructor Summary | |
Hashtable(int initialCapacity)
Constructs a new, empty hashtable with the specified initial capacity and default load factor of 0.75f. |
|
Hashtable(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 |
get(java.lang.String key)
Returns the value to which the specified key is mapped in this hashtable. |
Vector |
getKeys()
Return a Vector of the keys in the Hashtable. |
java.lang.Object |
put(java.lang.String key,
java.lang.Object value)
Maps the specified key to the specified
value in this hashtable. |
protected void |
rehash()
Rehashes the contents of the hashtable into a hashtable with a larger capacity. |
java.lang.Object |
remove(java.lang.String key)
Removes the key (and its corresponding value) from this hashtable. |
int |
size()
Returns the number of keys in this hashtable. |
java.lang.String |
toString()
Returns a rather long string representation of this hashtable. |
Methods inherited from class java.lang.Object |
hashCode |
Constructor Detail |
public Hashtable(int initialCapacity)
initialCapacity
- the initial capacity of the hashtable.public Hashtable(int initialCapacity, float loadFactor)
initialCapacity
- the initial capacity of the hashtable.loadFactor
- a number between 0.0 and 1.0.Method Detail |
public void clear()
public java.lang.Object get(java.lang.String key)
key
- a key in the hashtable.null
if the key is not mapped to any value in
this hashtable.java.util.Hashtable#put(java.lang.Object, java.lang.Object)
public Vector getKeys()
public java.lang.Object put(java.lang.String key, 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.
key
- the hashtable key.value
- the value.null
if it did not have one.java.lang.Object#equals(java.lang.Object)
,
java.util.Hashtable#get(java.lang.Object)
protected void rehash()
public java.lang.Object remove(java.lang.String key)
key
- the key that needs to be removed.null
if the key did not have a mapping.public int size()
public java.lang.String toString()
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