org.apache.xml.dtm.ref
Class DTMStringPool

java.lang.Object
  extended byorg.apache.xml.dtm.ref.DTMStringPool
Direct Known Subclasses:
CustomStringPool, DTMSafeStringPool

public class DTMStringPool
extends Object

DTMStringPool is an "interning" mechanism for strings. It will create a stable 1:1 mapping between a set of string values and a set of integer index values, so the integers can be used to reliably and uniquely identify (and when necessary retrieve) the strings.

Design Priorities:

Implementation detail: A standard Hashtable is relatively inefficient when looking up primitive int values, especially when we're already maintaining an int-to-string vector. So I'm maintaining a simple hash chain within this class.

NOTE: There is nothing in the code that has a real dependency upon String. It would work with any object type that implements reliable .hashCode() and .equals() operations. The API enforces Strings because it's safer that way, but this could trivially be turned into a general ObjectPool if one was needed.

Status: Passed basic test in main().


Field Summary
(package private) static int HASHPRIME
           
(package private)  IntVector m_hashChain
           
(package private)  int[] m_hashStart
           
(package private)  Vector m_intToString
           
static int NULL
           
 
Constructor Summary
DTMStringPool()
           
 
Method Summary
 String indexToString(int i)
           
static void main(String[] args)
          Command-line unit test driver.
 void removeAllElements()
           
 int stringToIndex(String s)
           
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

m_intToString

Vector m_intToString

HASHPRIME

static final int HASHPRIME
See Also:
Constant Field Values

m_hashStart

int[] m_hashStart

m_hashChain

IntVector m_hashChain

NULL

public static final int NULL
See Also:
Constant Field Values
Constructor Detail

DTMStringPool

public DTMStringPool()
Method Detail

removeAllElements

public void removeAllElements()

indexToString

public String indexToString(int i)
                     throws ArrayIndexOutOfBoundsException
Returns:
string whose value is uniquely identified by this integer index.
Throws:
ArrayIndexOutOfBoundsException - if index doesn't map to a string.

stringToIndex

public int stringToIndex(String s)
Returns:
integer index uniquely identifying the value of this string.

main

public static void main(String[] args)
Command-line unit test driver. This test relies on the fact that this version of the pool assigns indices consecutively, starting from zero, as new unique strings are encountered.