java.lang.Object | |
↳ | org.apache.xerces.util.SymbolTable |
Known Direct Subclasses |
This class is a symbol table implementation that guarantees that
strings used as identifiers are unique references. Multiple calls
to 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.
Nested Classes | |||||||||||
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SymbolTable.Entry | This class is a symbol table entry. |
Constants | |||||||||||
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int | TABLE_SIZE | Default table size. |
Fields | |||||||||||
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fBuckets | Buckets. | ||||||||||
fCount | The total number of entries in the hash table. | ||||||||||
fLoadFactor | The load factor for the SymbolTable. | ||||||||||
fTableSize | actual table size | ||||||||||
fThreshold | The table is rehashed when its size exceeds this threshold. |
Public Constructors | |||||||||||
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Constructs a new, empty SymbolTable with the specified initial
capacity and the specified load factor.
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Constructs a new, empty SymbolTable with the specified initial capacity
and default load factor, which is 0.75.
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Constructs a new, empty SymbolTable with a default initial capacity (101)
and load factor, which is 0.75.
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Public Methods | |||||||||||
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Adds the specified symbol to the symbol table and returns a
reference to the unique symbol.
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Adds the specified symbol to the symbol table and returns a
reference to the unique symbol.
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Returns true if the symbol table already contains the specified
symbol.
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Returns true if the symbol table already contains the specified
symbol.
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Returns a hashcode value for the specified symbol information.
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Returns a hashcode value for the specified symbol.
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Protected Methods | |||||||||||
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Increases the capacity of and internally reorganizes this
SymbolTable, in order to accommodate and access its entries more
efficiently.
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[Expand]
Inherited Methods | |||||||||||
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From class
java.lang.Object
|
Default table size.
The total number of entries in the hash table.
The load factor for the SymbolTable.
actual table size
The table is rehashed when its size exceeds this threshold. (The value of this field is (int)(capacity * loadFactor).)
Constructs a new, empty SymbolTable with the specified initial capacity and the specified load factor.
initialCapacity | the initial capacity of the SymbolTable. |
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loadFactor | the load factor of the SymbolTable. |
IllegalArgumentException | if the initial capacity is less than zero, or if the load factor is nonpositive. |
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Constructs a new, empty SymbolTable with the specified initial capacity and default load factor, which is 0.75.
initialCapacity | the initial capacity of the hashtable. |
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IllegalArgumentException | if the initial capacity is less than zero. |
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Constructs a new, empty SymbolTable with a default initial capacity (101) and load factor, which is 0.75.
Adds the specified symbol to the symbol table and returns a reference to the unique symbol. If the symbol already exists, the previous symbol reference is returned instead, in order guarantee that symbol references remain unique.
buffer | The buffer containing the new symbol. |
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offset | The offset into the buffer of the new symbol. |
length | The length of the new symbol in the buffer. |
Adds the specified symbol to the symbol table and returns a reference to the unique symbol. If the symbol already exists, the previous symbol reference is returned instead, in order guarantee that symbol references remain unique.
symbol | The new symbol. |
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Returns true if the symbol table already contains the specified symbol.
buffer | The buffer containing the symbol to look for. |
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offset | The offset into the buffer. |
length | The length of the symbol in the buffer. |
Returns true if the symbol table already contains the specified symbol.
symbol | The symbol to look for. |
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Returns a hashcode value for the specified symbol information.
The value returned by this method must be identical to the value
returned by the hash(String)
method when called
with the string object created from the symbol information.
buffer | The character buffer containing the symbol. |
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offset | The offset into the character buffer of the start of the symbol. |
length | The length of the symbol. |
Returns a hashcode value for the specified symbol. The value
returned by this method must be identical to the value returned
by the hash(char[],int,int)
method when called
with the character array that comprises the symbol string.
symbol | The symbol to hash. |
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Increases the capacity of and internally reorganizes this SymbolTable, in order to accommodate and access its entries more efficiently. This method is called automatically when the number of keys in the SymbolTable exceeds this hashtable's capacity and load factor.