Class DTMStringPool

java.lang.Object
org.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:

  • String-to-index lookup speed is critical.
  • Index-to-String lookup speed is slightly less so.
  • Threadsafety is not guaranteed at this level. Enforce that in the application if needed.
  • Storage efficiency is an issue but not a huge one. It is expected that string pools won't exceed about 2000 entries.

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 Details

  • Constructor Details

    • 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 Details

    • 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.