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java.lang.Object | +--org.apache.xerces.util.SymbolTable
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.
SymbolHash| Inner 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()
Constructs a new, empty SymbolTable with a default initial capacity (101) and load factor, which is 0.75. |
|
SymbolTable(int initialCapacity)
Constructs a new, empty SymbolTable with the specified initial capacity and default load factor, which is 0.75. |
|
SymbolTable(int initialCapacity,
float loadFactor)
Constructs a new, empty SymbolTable with the specified initial capacity and the specified load factor. |
|
| Method Summary | |
java.lang.String |
addSymbol(char[] buffer,
int offset,
int length)
Adds the specified symbol to the symbol table and returns a reference to the unique symbol. |
java.lang.String |
addSymbol(java.lang.String symbol)
Adds the specified symbol to the symbol table and returns a reference to the unique symbol. |
boolean |
containsSymbol(char[] buffer,
int offset,
int length)
Returns true if the symbol table already contains the specified symbol. |
boolean |
containsSymbol(java.lang.String symbol)
Returns true if the symbol table already contains the specified symbol. |
int |
hash(char[] buffer,
int offset,
int length)
Returns a hashcode value for the specified symbol information. |
int |
hash(java.lang.String symbol)
Returns a hashcode value for the specified symbol. |
protected void |
rehash()
Increases the capacity of and internally reorganizes this SymbolTable, in order to accommodate and access its entries more efficiently. |
| Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Field Detail |
protected static final int TABLE_SIZE
protected SymbolTable.Entry[] fBuckets
protected int fTableSize
protected transient int fCount
protected int fThreshold
protected float fLoadFactor
| Constructor Detail |
public SymbolTable(int initialCapacity,
float loadFactor)
initialCapacity - the initial capacity of the SymbolTable.loadFactor - the load factor of the SymbolTable.java.lang.IllegalArgumentException - if the initial capacity is less
than zero, or if the load factor is nonpositive.public SymbolTable(int initialCapacity)
initialCapacity - the initial capacity of the hashtable.java.lang.IllegalArgumentException - if the initial capacity is less
than zero.public SymbolTable()
| Method Detail |
public java.lang.String addSymbol(java.lang.String symbol)
symbol - The new symbol.
public java.lang.String addSymbol(char[] buffer,
int offset,
int length)
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.public int hash(java.lang.String symbol)
hash(char[],int,int) method when called
with the character array that comprises the symbol string.symbol - The symbol to hash.
public int hash(char[] buffer,
int offset,
int length)
hash(String) method when called
with the string object created from the symbol information.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.protected void rehash()
public boolean containsSymbol(java.lang.String symbol)
symbol - The symbol to look for.
public boolean containsSymbol(char[] buffer,
int offset,
int length)
buffer - The buffer containing the symbol to look for.offset - The offset into the buffer.length - The length of the symbol in the buffer.
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