Examples of java.util.IdentityHashMap

java.util.IdentityHashMap
This class implements the Map interface with a hash table, using reference-equality in place of object-equality when comparing keys (and values). In other words, in an IdentityHashMap, two keys k1 and k2 are considered equal if and only if (k1==k2). (In normal Map implementations (like HashMap) two keys k1 and k2 are considered equal if and only if (k1==null ? k2==null : k1.equals(k2)).)
This class is not a general-purpose Map implementation! While this class implements the Map interface, it intentionally violates Map's general contract, which mandates the use of the equals method when comparing objects. This class is designed for use only in the rare cases wherein reference-equality semantics are required.
A typical use of this class is topology-preserving object graph transformations, such as serialization or deep-copying. To perform such a transformation, a program must maintain a "node table" that keeps track of all the object references that have already been processed. The node table must not equate distinct objects even if they happen to be equal. Another typical use of this class is to maintain proxy objects. For example, a debugging facility might wish to maintain a proxy object for each object in the program being debugged.
This class provides all of the optional map operations, and permits null values and the null key. This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time.
This class provides constant-time performance for the basic operations (get and put), assuming the system identity hash function ( {@link System#identityHashCode(Object)}) disperses elements properly among the buckets.
This class has one tuning parameter (which affects performance but not semantics): expected maximum size. This parameter is the maximum number of key-value mappings that the map is expected to hold. Internally, this parameter is used to determine the number of buckets initially comprising the hash table. The precise relationship between the expected maximum size and the number of buckets is unspecified.
If the size of the map (the number of key-value mappings) sufficiently exceeds the expected maximum size, the number of buckets is increased Increasing the number of buckets ("rehashing") may be fairly expensive, so it pays to create identity hash maps with a sufficiently large expected maximum size. On the other hand, iteration over collection views requires time proportional to the number of buckets in the hash table, so it pays not to set the expected maximum size too high if you are especially concerned with iteration performance or memory usage.
Note that this implementation is not synchronized. If multiple threads access an identity hash map concurrently, and at least one of the threads modifies the map structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more mappings; merely changing the value associated with a key that an instance already contains is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the map. If no such object exists, the map should be "wrapped" using the {@link Collections#synchronizedMap Collections.synchronizedMap}method. This is best done at creation time, to prevent accidental unsynchronized access to the map:
```
 Map m = Collections.synchronizedMap(new IdentityHashMap(...));
```
The iterators returned by the iterator method of the collections returned by all of this class's "collection view methods" are fail-fast: if the map is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will throw a {@link ConcurrentModificationException}. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.
Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: fail-fast iterators should be used only to detect bugs.
Implementation note: This is a simple linear-probe hash table, as described for example in texts by Sedgewick and Knuth. The array alternates holding keys and values. (This has better locality for large tables than does using separate arrays.) For many JRE implementations and operation mixes, this class will yield better performance than {@link HashMap} (which uses chaining rather than linear-probing).
This class is a member of the Java Collections Framework. @see System#identityHashCode(Object) @see Object#hashCode() @see Collection @see Map @see HashMap @see TreeMap @author Doug Lea and Josh Bloch @since 1.4

  private IdentityHashMap lpDB;   //K: LogicalProcess  E: null
  private Executive exec;


  public CachingPopulationManager() {
    super();
    popMap = new IdentityHashMap();
    lpDB = new IdentityHashMap();
  }

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   * @see org.mitre.sim.exec.flex.PopulationManager#createPopulation(java.lang.Class)
   */
  public Population createPopulation(Class c) {
    CachedPopulation cp = (CachedPopulation)popMap.get(c);
    if (cp == null) {
      IdentityHashMap contents = new IdentityHashMap();
      for (Iterator i = lpDB.keySet().iterator(); i.hasNext(); ) {
        LogicalProcess lp = (LogicalProcess)i.next();
        if (c.isInstance(lp)) contents.put(lp, null);
      }
      cp = new CachedPopulation(contents);
      popMap.put(c, cp);
    }
    return cp;

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    this.baseClass = baseClass;
  }


  protected IdentityHashMap compute() {
    Set lpDB = myExec.getLogicalProcesses();
    IdentityHashMap partialDB = new IdentityHashMap();
    for (Iterator i = lpDB.iterator(); i.hasNext(); ) {
      Entity e = (Entity)i.next();
      if (baseClass.isInstance(e)) partialDB.put(e, null);
    }
    return partialDB;
  }

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   * @return the new Map instance
   * @deprecated as of Spring 2.5, for usage on JDK 1.4 or higher
   */
  @Deprecated
  public static Map createIdentityMapIfPossible(int initialCapacity) {
    return new IdentityHashMap(initialCapacity);
  }

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   * @param initialCapacity the initial capacity of the Map
   * @return the new Map instance
   * @deprecated as of Spring 2.5, for usage on JDK 1.4 or higher
   */
  public static Map createIdentityMapIfPossible(int initialCapacity) {
    return new IdentityHashMap(initialCapacity);
  }

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    private static Map createLinkedHashMap(int initialCapacity) {
      return new LinkedHashMap(initialCapacity);
    }


    private static Map createIdentityHashMap(int initialCapacity) {
      return new IdentityHashMap(initialCapacity);
    }

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  public void createWeight(Map context, Searcher searcher) throws IOException {
  }


  /** Returns a new non-threadsafe context map. */
  public static Map newContext() {
    return new IdentityHashMap();
  }

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    }


    void setDetailExpansionEnabled (boolean yn)
    {
        if (yn != detailExpansionEnabled()) {
            _detailRowExpansions = (yn) ? new IdentityHashMap() : null;
        }
    }

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            // Since _detailAttributesExpanded is an IdentityHashMap, on regroup,
            // we need to remap to the new group instances
            if (_detailAttributesExpanded.size() > 0) {
                Collection<PivotGroup> newGroups = _dataTable._displayGroup.groupingValueState().values();
                Set<PivotGroup> expanded = new HashSet(_detailAttributesExpanded.keySet());
                _detailAttributesExpanded = new IdentityHashMap();
                for (PivotGroup g : newGroups) {
                    if (expanded.contains(g)) _detailAttributesExpanded.put(g, true);
                }
            }
        }

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     */
    public void compareCollectionsForChange(Object oldList, Object newList, CollectionChangeRecord changeRecord, AbstractSession session, ClassDescriptor referenceDescriptor) {    
        Vector orderedObjectsToAdd = new Vector();
        Hashtable indicesToRemove = new Hashtable();
        Hashtable oldListIndexValue = new Hashtable();
        IdentityHashMap oldListValueIndex = new IdentityHashMap();
        IdentityHashMap objectsToAdd = new IdentityHashMap();
        IdentityHashtable newListValueIndex = new IdentityHashtable();
        
        // Step 1 - Go through the old list.
        if (oldList != null) {
            ListIterator iterator = iteratorFor(oldList);
        
            while (iterator.hasNext()) {
                Integer index = new Integer(iterator.nextIndex());
                Object value = iterator.next();
                oldListValueIndex.put(value, index);
                oldListIndexValue.put(index, value);
                indicesToRemove.put(index, index);
            }
        }
            
        // Step 2 - Go though the new list.
        if (newList != null) {
            // Step i - Gather the list info.
            ListIterator iterator = iteratorFor(newList);
            while (iterator.hasNext()) {
                newListValueIndex.put(iterator.next(), new Integer(iterator.previousIndex()));
            }
        
            // Step ii - Go through the new list again.        
            int index = 0;
            int offset = 0;
            iterator = iteratorFor(newList);
            while (iterator.hasNext()) {
                index = iterator.nextIndex();
                Object currentObject = iterator.next();
            
                // If value is null then nothing can be done with it.
                if (currentObject != null) {
                    if (oldListValueIndex.containsKey(currentObject)) {
                        int oldIndex = ((Integer) oldListValueIndex.get(currentObject)).intValue();
                        oldListValueIndex.remove(currentObject);
                    
                        if (index == oldIndex) {
                            indicesToRemove.remove(new Integer(oldIndex));
                            offset = 0; // Reset the offset, assume we're back on track.
                        } else if (index == (oldIndex + offset)) {
                            // We're in the right spot according to the offset.
                            indicesToRemove.remove(new Integer(oldIndex));
                        } else {
                            // Time to be clever and figure out why we're not in the right spot!
                            int movedObjects = 0;
                            int deletedObjects = 0;
                            boolean moved = true;
                        
                            if (oldIndex < index) {
                                ++offset;    
                            } else {
                                for (int i = oldIndex - 1; i >= index; i--) {
                                    Object oldObject = oldListIndexValue.get(new Integer(i));
                                    if (newListValueIndex.containsKey(oldObject)) {
                                        ++movedObjects;
                                    } else {
                                        ++deletedObjects;
                                    }
                                }
                            
                                if (index == ((oldIndex + offset) - deletedObjects)) {
                                    // We fell into place because of deleted objects.
                                    offset = offset - deletedObjects;
                                    moved = false;
                                } else if (movedObjects > 1) {
                                    // Assume we moved down, bumping everyone by one. 
                                    ++offset;
                                } else {
                                    // Assume we moved down unless the object that was
                                    // here before is directly beside us.
                                    Object oldObject = oldListIndexValue.get(new Integer(index));
                                
                                    if (newListValueIndex.containsKey(oldObject)) {
                                        if ((((Integer) newListValueIndex.get(oldObject)).intValue() - index) > 1) {
                                            moved = false; // Assume the old object moved up.
                                            --offset; 
                                        }
                                    }
                                }
                            }
                        
                            if (moved) {
                                // Add ourselves to the ordered add list.
                                orderedObjectsToAdd.add(currentObject);
                            } else {
                                // Take us off the removed list.
                                indicesToRemove.remove(new Integer(oldIndex));    
                            }
                        }
                    } else {
                        ++offset;
                        objectsToAdd.put(currentObject, currentObject);
                        orderedObjectsToAdd.add(currentObject);
                    }
                } else {
                    // If we find nulls we need decrease our offset.
                    offset--;

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