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Class flybase.FastHashtable

java.lang.Object
   |
   +----java.util.Dictionary
           |
           +----flybase.FastHashtable

public class FastHashtable
extends java.util.Dictionary
implements java.lang.Cloneable, java.io.Serializable
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 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", 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);
     }
 

See Also:
equals, hashCode, rehash

Constructor Index

 o FastHashtable()
Constructs a new, empty hashtable with a default capacity and load factor.
 o FastHashtable(Hashtable)
 o FastHashtable(int)
Constructs a new, empty hashtable with the specified initial capacity and default load factor.
 o FastHashtable(int, float)
Constructs a new, empty hashtable with the specified initial capacity and the specified load factor.

Method Index

 o clear()
Clears this hashtable so that it contains no keys.
 o clone()
Creates a shallow copy of this hashtable.
 o contains(Object)
Tests if some key maps into the specified value in this hashtable.
 o containsKey(Object)
Tests if the specified object is a key in this hashtable.
 o elements()
Returns an enumeration of the values in this hashtable.
 o get(Object)
Returns the value to which the specified key is mapped in this hashtable.
 o isEmpty()
Tests if this hashtable maps no keys to values.
 o keys()
Returns an enumeration of the keys in this hashtable.
 o put(Object, Object)
Maps the specified key to the specified value in this hashtable.
 o remove(Object)
Removes the key (and its corresponding value) from this hashtable.
 o size()
Returns the number of keys in this hashtable.
 o toHashtable()
dgg additions
 o toString()
Returns a rather long string representation of this hashtable.

Constructors

 o FastHashtable
 public FastHashtable(int initialCapacity,
                      float loadFactor)
Constructs a new, empty hashtable with the specified initial capacity and the specified load factor.

Parameters:
initialCapacity - the initial capacity of the hashtable.
loadFactor - a number between 0.0 and 1.0.
Throws: IllegalArgumentException
if the initial capacity is less than or equal to zero, or if the load factor is less than or equal to zero.
 o FastHashtable
 public FastHashtable(int initialCapacity)
Constructs a new, empty hashtable with the specified initial capacity and default load factor.

Parameters:
initialCapacity - the initial capacity of the hashtable.
 o FastHashtable
 public FastHashtable()
Constructs a new, empty hashtable with a default capacity and load factor.

 o FastHashtable
 public FastHashtable(java.util.Hashtable jh)

Methods

 o toHashtable
 public java.util.Hashtable toHashtable()
dgg additions

 o size
 public int size()
Returns the number of keys in this hashtable.

Returns:
the number of keys in this hashtable.
Overrides:
size in class java.util.Dictionary
 o isEmpty
 public boolean isEmpty()
Tests if this hashtable maps no keys to values.

Returns:
true if this hashtable maps no keys to values; false otherwise.
Overrides:
isEmpty in class java.util.Dictionary
 o keys
 public java.util.Enumeration keys()
Returns an enumeration of the keys in this hashtable.

Returns:
an enumeration of the keys in this hashtable.
Overrides:
keys in class java.util.Dictionary
See Also:
java.util.Enumeration, elements
 o elements
 public java.util.Enumeration elements()
Returns an enumeration of the values in this hashtable. Use the Enumeration methods on the returned object to fetch the elements sequentially.

Returns:
an enumeration of the values in this hashtable.
Overrides:
elements in class java.util.Dictionary
See Also:
java.util.Enumeration, keys
 o contains
 public boolean contains(java.lang.Object value)
Tests if some key maps into the specified value in this hashtable. This operation is more expensive than the containsKey method.

Parameters:
value - a value to search for.
Returns:
true if some key maps to the value argument in this hashtable; false otherwise.
Throws: NullPointerException
if the value is null.
See Also:
containsKey
 o containsKey
 public boolean containsKey(java.lang.Object key)
Tests if the specified object is a key in this hashtable.

Parameters:
key - possible key.
Returns:
true if the specified object is a key in this hashtable; false otherwise.
See Also:
contains
 o get
 public java.lang.Object get(java.lang.Object key)
Returns the value to which the specified key is mapped in this hashtable.

Parameters:
key - a key in the hashtable.
Returns:
the value to which the key is mapped in this hashtable; null if the key is not mapped to any value in this hashtable.
Overrides:
get in class java.util.Dictionary
See Also:
put
 o put
 public java.lang.Object put(java.lang.Object key,
                             java.lang.Object value)
Maps the specified 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.

Parameters:
key - the hashtable key.
value - the value.
Returns:
the previous value of the specified key in this hashtable, or null if it did not have one.
Throws: NullPointerException
if the key or value is null.
Overrides:
put in class java.util.Dictionary
See Also:
equals, get
 o remove
 public java.lang.Object remove(java.lang.Object key)
Removes the key (and its corresponding value) from this hashtable. This method does nothing if the key is not in the hashtable.

Parameters:
key - the key that needs to be removed.
Returns:
the value to which the key had been mapped in this hashtable, or null if the key did not have a mapping.
Overrides:
remove in class java.util.Dictionary
 o clear
 public void clear()
Clears this hashtable so that it contains no keys.

 o clone
 public java.lang.Object clone()
Creates a shallow copy of this hashtable. The keys and values themselves are not cloned. This is a relatively expensive operation.

Returns:
a clone of the hashtable.
Overrides:
clone in class java.lang.Object
 o toString
 public java.lang.String toString()
Returns a rather long string representation of this hashtable.

Returns:
a string representation of this hashtable.
Overrides:
toString in class java.lang.Object

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