org.apache.xerces.util
public class SymbolTable extends Object
addSymbol
will always return the same string
reference.
The symbol table performs the same task as String.intern()
with the following differences:
SymbolTable
has two parameters that affect its
performance: initial capacity and load factor. The
capacity is the number of buckets in the SymbolTable, and the
initial capacity is simply the capacity at the time the SymbolTable
is created. Note that the SymbolTable 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 SymbolTable
is allowed to get before its capacity is automatically increased.
When the number of entries in the SymbolTable 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 SymbolTable operations, including addSymbol and containsSymbol).
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
Hashtable 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 SymbolTable
,
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.
Version: $Id: SymbolTable.java,v 1.10 2005/03/14 23:09:35 mrglavas Exp $
Nested Class Summary | |
---|---|
protected static class | SymbolTable.Entry
This class is a symbol table entry. |
Field Summary | |
---|---|
protected SymbolTable.Entry[] | fBuckets Buckets. |
protected int | fCount The total number of entries in the hash table. |
protected float | fLoadFactor The load factor for the SymbolTable. |
protected int | fTableSize actual table size * |
protected int | fThreshold The table is rehashed when its size exceeds this threshold. |
protected static int | TABLE_SIZE Default table size. |
Constructor Summary | |
---|---|
SymbolTable(int initialCapacity, float loadFactor)
Constructs a new, empty SymbolTable with the specified initial
capacity and the specified load factor.
| |
SymbolTable(int initialCapacity)
Constructs a new, empty SymbolTable with the specified initial capacity
and default load factor, which is 0.75.
| |
SymbolTable()
Constructs a new, empty SymbolTable with a default initial capacity (101)
and load factor, which is 0.75. |
Method Summary | |
---|---|
String | addSymbol(String symbol)
Adds the specified symbol to the symbol table and returns a
reference to the unique symbol. |
String | addSymbol(char[] buffer, int offset, int length)
Adds the specified symbol to the symbol table and returns a
reference to the unique symbol. |
boolean | containsSymbol(String symbol)
Returns true if the symbol table already contains the specified
symbol.
|
boolean | containsSymbol(char[] buffer, int offset, int length)
Returns true if the symbol table already contains the specified
symbol.
|
int | hash(String symbol)
Returns a hashcode value for the specified symbol. |
int | hash(char[] buffer, int offset, int length)
Returns a hashcode value for the specified symbol information.
|
protected void | rehash()
Increases the capacity of and internally reorganizes this
SymbolTable, in order to accommodate and access its entries more
efficiently. |
Parameters: initialCapacity the initial capacity of the SymbolTable. loadFactor the load factor of the SymbolTable.
Throws: IllegalArgumentException if the initial capacity is less than zero, or if the load factor is nonpositive.
Parameters: initialCapacity the initial capacity of the hashtable.
Throws: IllegalArgumentException if the initial capacity is less than zero.
Parameters: symbol The new symbol.
Parameters: buffer The buffer containing the new symbol. offset The offset into the buffer of the new symbol. length The length of the new symbol in the buffer.
Parameters: symbol The symbol to look for.
Parameters: buffer The buffer containing the symbol to look for. offset The offset into the buffer. length The length of the symbol in the buffer.
hash(char[],int,int)
method when called
with the character array that comprises the symbol string.
Parameters: symbol The symbol to hash.
hash(String)
method when called
with the string object created from the symbol information.
Parameters: buffer The character buffer containing the symbol. offset The offset into the character buffer of the start of the symbol. length The length of the symbol.