org.apache.xml.dtm.ref
Class DTMStringPool

java.lang.Object
  |
  +--org.apache.xml.dtm.ref.DTMStringPool
Direct Known Subclasses:
CustomStringPool, DTMSafeStringPool

public class DTMStringPool
extends java.lang.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
static int NULL
           
 
Constructor Summary
DTMStringPool()
           
DTMStringPool(int chainSize)
          Create a DTMStringPool using the given chain size
 
Method Summary
 java.lang.String indexToString(int i)
           
static void main(java.lang.String[] args)
          Command-line unit test driver.
 void removeAllElements()
           
 int stringToIndex(java.lang.String s)
           
 
Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

NULL

public static final int NULL
Constructor Detail

DTMStringPool

public DTMStringPool(int chainSize)
Create a DTMStringPool using the given chain size
Parameters:
chainSize - The size of the hash chain vector

DTMStringPool

public DTMStringPool()
Method Detail

removeAllElements

public void removeAllElements()

indexToString

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

stringToIndex

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

main

public static void main(java.lang.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.


Copyright 2006 Apache XML Project. All Rights Reserved.