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  1. JDK
  2. JDK-1250096

CacheEnumerator in sun.misc.Cache does not work

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    • Subcomponent:
    • Resolved In Build:
      1.1
    • CPU:
      generic
    • OS:
      solaris_2.4
    • Verification:
      Not verified

      Description

      [prasadw, pavani 960514 - later on that night :) ]

      The problem was in the following statement in hasMoreElements:
      while (--index >= 0 && (entry = table[index]) != null) ;
      The "!= null" should be "== null" since the objective is to skip over the null
      elements.


      [prasadw, pavani 960514]

      Here is a test program:

      $ more T.java
      import java.util.*;
      import sun.misc.Cache;

      class T {
          public static void main(String argv[]) {
              Cache numbers = new Cache();
              Enumeration enumElements;
              Enumeration enumKeys;
              Object object;

              numbers.put("one", new Integer(1));
              numbers.put("two", new Integer(1));
              numbers.put("three", new Integer(1));
              System.out.println("size = " + numbers.size());
              enumElements = numbers.elements();
              System.out.println("enumElements.hasMoreElements() = " +
                  enumElements.hasMoreElements());
              enumKeys = numbers.keys();
              System.out.println("enumKeys.hasMoreElements() = " +
                  enumKeys.hasMoreElements());
          }
      }
      $ javac T.java
      $ java T
      size = 3
      enumElements.hasMoreElements() = false
      enumKeys.hasMoreElements() = false


      The problem is that when the hasMoreElements function in CacheEnumerator
      is entered entry is not initialized.

      /**
       * A Cache enumerator class. This class should remain opaque
       * to the client. It will use the Enumeration interface.
       */
      class CacheEnumerator implements Enumeration {
          boolean keys;
          int index;
          CacheEntry table[];
          CacheEntry entry;

          CacheEnumerator (CacheEntry table[], boolean keys) {
              this.table = table;
              this.keys = keys;
              this.index = table.length;
          }
       
          public boolean hasMoreElements() {
              while (index >= 0) {
                  while (entry != null)
                      if (entry.check() != null)
                          return true;
                      else
                          entry = entry.next;
                  while (--index >= 0 && (entry = table[index]) != null) ;
              }
              return false;
          }

          public Object nextElement() {
              while (index >= 0) {
                  if (entry == null)
                      while (--index >= 0 && (entry = table[index]) == null) ;
                  if (entry != null) {
                      CacheEntry e = entry;
                      entry = e.next;
                      if (e.check() != null)
                          return keys ? e.key : e.check();
                  }
              }
              throw new NoSuchElementException("CacheEnumerator");
          }

      }

      Changing the constructor as follows seems to fix the problem, though we
      haven't tested it thoroughly. Also it would be helpful to comment on the
      logic.

          CacheEnumerator (CacheEntry table[], boolean keys) {
              System.out.println("table.length = " + table.length);
              this.table = table;
              this.keys = keys;
              this.index = table.length - 1;
              this.entry = table[index];
          }

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            Assignee:
            tlindholsunw Timothy Lindholm (Inactive)
            Reporter:
            duke J. Duke (Inactive)
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