Package ca.odell.glazedlists

Class GlazedLists

  • public final class GlazedLists
extends java.lang.Object
    A factory for creating all sorts of objects to be used with Glazed Lists.
    Author:
    Jesse Wilson

    • Method Detail

      • replaceAll

        public static <E> void replaceAll​(EventList<E> target,
                                  java.util.List<E> source,
                                  boolean updates)
        Replace the complete contents of the target EventList with the complete contents of the source EventList while making as few list changes as possible.

        In a multi-threaded environment, it is necessary that the caller obtain the write lock for the target list before this method is invoked. If the source list is an EventList, its read lock must also be acquired.

        This method shall be used when it is necessary to update an EventList to a newer state while minimizing the number of change events fired. It is desirable over clear(); addAll() because it will not cause selection to be lost if unnecessary. It is also useful where firing changes may be expensive, such as when they will cause writes to disk or the network.

        This is implemented using Eugene W. Myer's paper, "An O(ND) Difference Algorithm and Its Variations", the same algorithm found in GNU diff.

        Note that the runtime of this method is significantly less efficient in both time and memory than the sorted version of replaceAll.

        Parameters:
        updates - whether to fire update events for Objects that are equal in both Lists.

      • replaceAll

        public static <E> void replaceAll​(EventList<E> target,
                                  java.util.List<E> source,
                                  boolean updates,
                                  java.util.Comparator<E> comparator)
        Overloaded version of replaceAll(EventList,List,boolean) that uses a Comparator to determine equality rather than equals().
        Parameters:
        comparator - the Comparator to determine equality between elements. This Comparator must return 0 for elements that are equal and nonzero for elements that are not equal. Sort order is not used.

      • replaceAllSorted

        public static <E> void replaceAllSorted​(EventList<E> target,
                                        java.util.Collection<E> source,
                                        boolean updates,
                                        java.util.Comparator<E> comparator)
        Replace the complete contents of the target EventList with the complete contents of the source Collection while making as few list changes as possible.

        Unlike the general versions of this method, the sorted version requires that both the input and the output are sorted collections, and that they're sorted with the Comparator specified. If they're sorted in natural order, use comparableComparator().

        In a multi-threaded environment, it is necessary that the caller obtain the write lock for the target list before this method is invoked. If the source list is an EventList, its read lock must also be acquired.

        This method shall be used when it is necessary to update an EventList to a newer state while minimizing the number of change events fired. It is desirable over clear(); addAll() because it will not cause selection to be lost if unnecessary. It is also useful where firing changes may be expensive, such as when they will cause writes to disk or the network.

        Note that this method is significantly more efficient in both time and memory than the general version of replaceAll.

        Parameters:
        target - an EventList sorted with the Comparator specified. Its contents will be replaced with those in source.
        source - a collection sorted with the Comparator specified.
        comparator - defines the sort order for both target and source. It should also define identity. Ie, elements that compare to 0 by this comparator represent the same logical element in the list. If null, the comparableComparator will be used, which means that all elements must implement Comparable.
        updates - whether to fire update events for Objects that are equal in both Lists.
        See Also:
        Collections.sort(java.util.List<T>), SortedSet

      • beanPropertyComparator

        public static <T> java.util.Comparator<T> beanPropertyComparator​(java.lang.Class<T> clazz,
                                                                 java.lang.String property,
                                                                 java.lang.String... properties)
        Creates a Comparator that uses Reflection to compare two instances of the specified Class by the given JavaBean properties. The JavaBean property and any extra properties must implement Comparable.

        The following example code sorts a List of Customers by first name, with ties broken by last name. 

            List customers = ...
    Comparator comparator = GlazedLists.beanPropertyComparator(Customer.class, "firstName", "lastName");
    Collections.sort(customers, comparator);
        Parameters:
        clazz - the name of the class which defines the accessor method for the given property and optionaly properties
        property - the name of the first Comparable property to be extracted and used to compare instances of the clazz
        properties - the name of optional Comparable properties, each of which is used to break ties for the prior property.

      • beanPropertyComparator

        public static <T> java.util.Comparator<T> beanPropertyComparator​(java.lang.Class<T> className,
                                                                 java.lang.String property,
                                                                 java.util.Comparator propertyComparator)
        Creates a Comparator that uses Reflection to compare two instances of the specified Class by the given JavaBean property. The JavaBean property is compared using the provided Comparator.

      • booleanComparator

        public static java.util.Comparator<java.lang.Boolean> booleanComparator()
        Creates a Comparator for use with Boolean objects.

      • caseInsensitiveComparator

        public static java.util.Comparator<java.lang.String> caseInsensitiveComparator()
        Creates a Comparator that compares String objects in a case-insensitive way. This Comparator is equivalent to using String.CASE_INSENSITIVE_ORDER and exists here for convenience.

      • chainComparators

        public static <T> java.util.Comparator<T> chainComparators​(java.util.List<java.util.Comparator<T>> comparators)
        Creates a chain of Comparators that applies the provided Comparators in the sequence specified until differences or absolute equality is determined.

      • chainComparators

        public static <T> java.util.Comparator<T> chainComparators​(java.util.Comparator<T>... comparators)
        Creates a chain of Comparators that applies the provided Comparators in the sequence specified until differences or absolute equality is determined.

      • comparableComparator

        public static <T extends java.lang.Comparable> java.util.Comparator<T> comparableComparator()
        Creates a Comparator that compares Comparable objects.

      • reverseComparator

        public static <T extends java.lang.Comparable> java.util.Comparator<T> reverseComparator()
        Creates a reverse Comparator that works for Comparable objects.

      • reverseComparator

        public static <T> java.util.Comparator<T> reverseComparator​(java.util.Comparator<T> forward)
        Creates a reverse Comparator that inverts the given Comparator.

      • tableFormat

        public static <T> TableFormat<T> tableFormat​(java.lang.String[] propertyNames,
                                             java.lang.String[] columnLabels)
        Creates a TableFormat that binds JavaBean properties to table columns via Reflection.

      • tableFormat

        public static <T> TableFormat<T> tableFormat​(java.lang.String[] propertyNames,
                                             java.lang.String[] columnLabels,
                                             boolean[] editable)
        Creates a TableFormat that binds JavaBean properties to table columns via Reflection. The returned TableFormat implements WritableTableFormat and may be used for an editable table.

      • textFilterator

        public static <E> TextFilterator<E> textFilterator​(java.lang.String... propertyNames)
        Creates a TextFilterator that searches the given JavaBean properties.

      • textFilterator

        public static <E> TextFilterator<E> textFilterator​(java.lang.Class<E> beanClass,
                                                   java.lang.String... propertyNames)
        Creates a TextFilterator that searches the given JavaBean properties.

      • filterator

        public static <D,​E> Filterator<D,​E> filterator​(java.lang.String... propertyNames)
        Creates a TextFilterator that searches the given JavaBean properties.

      • filterator

        public static <D,​E> Filterator<D,​E> filterator​(java.lang.Class<E> beanClass,
                                                           java.lang.String... propertyNames)
        Creates a TextFilterator that searches the given JavaBean properties of the specified class.

      • toStringTextFilterator

        public static <E> TextFilterator<E> toStringTextFilterator()
        Creates a TextFilterator that searches against an Object's toString() value.

      • thresholdEvaluator

        public static <E> ThresholdList.Evaluator<E> thresholdEvaluator​(java.lang.String propertyName)
        Creates a ThresholdList.Evaluator that uses Reflection to utilize an integer JavaBean property as the threshold evaluation.

      • eventListOf

        public static <E> EventList<E> eventListOf​(E... contents)
        Creates a new EventList which contains the given elements.
        Parameters:
        contents - the list elements, if null the result will be an empty list
        Returns:
        the new EventList

      • eventList

        public static <E> EventList<E> eventList​(java.util.Collection<? extends E> contents)
        Creates a new EventList which contains the contents of the specified Collection. The EventList's order will be determined by contents.iterator().
        Parameters:
        contents - the collection with list elements, if null the result will be an empty list

      • readOnlyList

        public static <E> TransformedList<E,​E> readOnlyList​(EventList<? extends E> source)
        Wraps the source in an EventList that does not allow writing operations.

        The returned EventList is useful for programming defensively. A EventList is useful to supply an unknown class read-only access to your EventList.

        The returned EventList will provides an up-to-date view of its source EventList so changes to the source EventList will still be reflected. For a static copy of any EventList it is necessary to copy the contents of that EventList into an ArrayList.

        Warning: This returned EventList is thread ready but not thread safe. See EventList for an example of thread safe code.

      • threadSafeList

        public static <E> TransformedList<E,​E> threadSafeList​(EventList<? extends E> source)
        Wraps the source in an EventList that obtains a ReadWritLock for all operations.

        This provides some support for sharing EventLists between multiple threads.

        Using a ThreadSafeList for concurrent access to lists can be expensive because a ReadWriteLock is aquired and released for every operation.

        Warning: Although this class provides thread safe access, it does not provide any guarantees that changes will not happen between method calls. For example, the following code is unsafe because the source EventList may change between calls to size() and get(): 

         EventList source = ...
 ThreadSafeList myList = new ThreadSafeList(source);
 if(myList.size() > 3) {
   System.out.println(myList.get(3));
 }

        Warning: The objects returned by iterator(), subList(), etc. are not thread safe.

        See Also:
        ca.odell.glazedlists.util.concurrent

      • transformByFunction

        public static <S,​E> TransformedList<S,​E> transformByFunction​(EventList<S> source,
                                                                         FunctionList.Function<S,​E> function)
        Returns a TransformedList that maps each element of the source list to a target element by use of a specified FunctionList.Function.

        Warning: The returned EventList is thread ready but not thread safe. See EventList for an example of thread safe code.

        Warning:This method will not return a full-featured FunctionList, but a much simpler list implementation, that is not writable.

        Parameters:
        source - the source list to transform
        function - the function to tranform each list element
        Returns:
        a TransformedList that needs to be disposed after use

      • weakReferenceProxy

        public static <E> ListEventListener<E> weakReferenceProxy​(EventList<E> source,
                                                          ListEventListener<E> target)
        Provides a proxy to another ListEventListener that may go out of scope without explicitly removing itself from the source list's set of listeners.

        This exists to solve a garbage collection problem. Suppose I have an EventList L and I obtain a ListIterator for L. The ListIterator must listen for change events to L in order to be consistent. Therefore such an iterator will register itself as a listener for L. When the iterator goes out of scope (as they usually do), it will remain as a listener of L. This prevents the iterator object from ever being garbage collected, though the iterator can never be never used again! Because iterators can be used very frequently, this will cause an unacceptable memory leak.

        Instead of adding the iterator directly as a listener for L, add a proxy instead. The proxy will retain a WeakReference to the iterator and forward events to the iterator as long as it is reachable. When the iterator is no longer reachable, the proxy will remove itself from the list of listeners for L. All garbage is then available for collection.

        See Also:
        WeakReference

      • beanConnector

        public static <E> ObservableElementList.Connector<E> beanConnector​(java.lang.Class<E> beanClass)
        Create a new Connector for the ObservableElementList that works with JavaBeans' PropertyChangeListener. The methods to add and remove listeners are detected automatically by examining the bean class and searching for a method prefixed with "add" or "remove" taking a single PropertyChangeListener argument.
        Parameters:
        beanClass - a class with both addPropertyChangeListener(PropertyChangeListener) and removePropertyChangeListener(PropertyChangeListener), or similar methods.
        Returns:
        an ObservableElementList.Connector for the specified class

      • beanConnector

        public static <E> ObservableElementList.Connector<E> beanConnector​(java.lang.Class<E> beanClass,
                                                                   boolean matchPropertyNames,
                                                                   java.lang.String... propertyNames)
        Create a new Connector for the ObservableElementList that works with JavaBeans' PropertyChangeListener. The methods to add and remove listeners are detected automatically by examining the bean class and searching for a method prefixed with "add" or "remove" taking a single PropertyChangeListener argument.

        Use this variant, if you want to control which PropertyChangeEvents are delivered to the ObservableElementList. You can match or filter events by name.

        If matchPropertyNames is true, the propertyNames parameter specifies the set of properties by name whose PropertyChangeEvents should be delivered to the ObservableElementList, e.g. property change events for properties not contained in the specified propertyNames are ignored in this case. If matchPropertyNames is false, then the specified propertyNames are filtered, e.g. all but the specified property change events are delivered to the ObservableElementList.

        Parameters:
        beanClass - a class with both addPropertyChangeListener(PropertyChangeListener) and removePropertyChangeListener(PropertyChangeListener), or similar methods.
        matchPropertyNames - if true, match property change events against the specified property names, if false filter them
        propertyNames - specifies the properties by name whose PropertyChangeEvents should be matched or filtered
        Returns:
        an ObservableElementList.Connector for the specified class

      • beanConnector

        public static <E> ObservableElementList.Connector<E> beanConnector​(java.lang.Class<E> beanClass,
                                                                   Matcher<java.beans.PropertyChangeEvent> eventMatcher)
        Create a new Connector for the ObservableElementList that works with JavaBeans' PropertyChangeListener. The methods to add and remove listeners are detected automatically by examining the bean class and searching for a method prefixed with "add" or "remove" taking a single PropertyChangeListener argument.

        The event matcher allows filtering of PropertyChangeEvents. Only matching events are delivered to the ObservableElementList. To create a matcher that matches PropertyChangeEvents by property names, you can use Matchers.propertyEventNameMatcher(boolean, String[])

        Parameters:
        beanClass - a class with both addPropertyChangeListener(PropertyChangeListener) and removePropertyChangeListener(PropertyChangeListener), or similar methods.
        eventMatcher - for matching PropertyChangeEvents that will be delivered to the ObservableElementList
        Returns:
        an ObservableElementList.Connector for the specified class

      • beanConnector

        public static <E> ObservableElementList.Connector<E> beanConnector​(java.lang.Class<E> beanClass,
                                                                   java.lang.String addListener,
                                                                   java.lang.String removeListener)
        Create a new Connector for the ObservableElementList that works with JavaBeans' PropertyChangeListener. The methods to add and remove listeners are specified by name. Such methods must take a single PropertyChangeListener argument.
        Parameters:
        beanClass - a class with both methods as specified.
        addListener - a method name such as "addPropertyChangeListener"
        removeListener - a method name such as "removePropertyChangeListener"
        Returns:
        an ObservableElementList.Connector for the specified class

      • beanConnector

        public static <E> ObservableElementList.Connector<E> beanConnector​(java.lang.Class<E> beanClass,
                                                                   java.lang.String addListener,
                                                                   java.lang.String removeListener,
                                                                   Matcher<java.beans.PropertyChangeEvent> eventMatcher)
        Create a new Connector for the ObservableElementList that works with JavaBeans' PropertyChangeListener. The methods to add and remove listeners are specified by name. Such methods must take a single PropertyChangeListener argument.

        The event matcher allows filtering of PropertyChangeEvents. Only matching events are delivered to the ObservableElementList. To create a matcher that matches PropertyChangeEvents by property names, you can use Matchers.propertyEventNameMatcher(boolean, String[])

        Parameters:
        beanClass - a class with both methods as specified.
        addListener - a method name such as "addPropertyChangeListener"
        removeListener - a method name such as "removePropertyChangeListener"
        eventMatcher - for matching PropertyChangeEvents that will be delivered to the ObservableElementList
        Returns:
        an ObservableElementList.Connector for the specified class

      • observableConnector

        public static <E extends java.util.Observable> ObservableElementList.Connector<E> observableConnector()
        Create a new Connector for the ObservableElementList that works with subclasses of the archaic Observable base class. Each element of the ObservableElementList must extend the Observable base class.
        Returns:
        an ObservableElementList.Connector for objects that extend Observable

      • beanPropertyMatcher

        public static <E> Matcher<E> beanPropertyMatcher​(java.lang.Class<E> beanClass,
                                                 java.lang.String propertyName,
                                                 java.lang.Object value)
        Deprecated.
        as of 3/3/2006 - this method has been replaced by Matchers.beanPropertyMatcher(java.lang.Class<E>, java.lang.String, java.lang.Object). Matchers is now the permanent factory class which creates all basic Matcher implementations.
        Create a new Matcher which uses reflection to read properties with the given propertyName from instances of the given beanClass and compare them with the given value.
        Parameters:
        beanClass - the type of class containing the named bean property
        propertyName - the name of the bean property
        value - the value to compare with the bean property
        Returns:
        true if the named bean property equals the given value

      • toStringFunction

        public static <E> FunctionList.Function<E,​java.lang.String> toStringFunction​(java.lang.Class<E> beanClass,
                                                                                   java.lang.String propertyName)
        Get a FunctionList.Function that extracts the property with the given propertyName from objects of the given beanClass and then formats the return value as a String.

      • beanFunction

        public static <E,​V> FunctionList.Function<E,​V> beanFunction​(java.lang.Class<E> beanClass,
                                                                        java.lang.String propertyName)
        Get a FunctionList.Function that extracts the property with the given propertyName from objects of the given beanClass.

      • syncEventListToList

        public static <E> ListEventListener<E> syncEventListToList​(EventList<E> source,
                                                           java.util.List<E> target)
        Synchronize the specified EventList to the specified List. Each time the EventList is changed, the changes are applied to the List as well, so that the two lists are always equal.

        This is useful when a you need to support a List datamodel but would prefer to manipulate that List with the convenience of EventLists: 

        List someList = ...

 // create an EventList with the contents of someList
 EventList eventList = GlazedLists.eventList(someList);

 // propagate changes from eventList to someList
 GlazedLists.syncEventListToList(eventList, someList);

 // test it out, should print "true, true, true true"
 eventList.add("boston creme");
 System.out.println(eventList.equals(someList));
 eventList.add("crueller");
 System.out.println(eventList.equals(someList));
 eventList.remove("bostom creme");
 System.out.println(eventList.equals(someList));
 eventList.clear();
 System.out.println(eventList.equals(someList));
        Parameters:
        source - the EventList which provides the master view. Each change to this EventList will be applied to the List.
        target - the List to host a copy of the EventList. This List should not be changed after the lists have been synchronized. Otherwise a RuntimeException will be thrown when the drift is detected. This class must support all mutating List operations.
        Returns:
        the ListEventListener providing the link from the source EventList to the target List. To stop the synchronization, use EventList.removeListEventListener(ListEventListener).

      • typeSafetyListener

        public static <E> ListEventListener<E> typeSafetyListener​(EventList<E> source,
                                                          java.util.Set<java.lang.Class> types)
        Check list elements for type safety after they are added to an EventList using a ListEventListener. The ListEventListener which is installed and returned to the caller (which they may uninstall at their leisure) will throw an IllegalArgumentException if it detects the addition of an element with an unsupported type.

        This ListEventListener is typically used as a tool to check invariants of the elements of EventLists during software development and testing phases.

        Parameters:
        source - the EventList on which to provide type safety
        types - the set of types to which each list element must be assignable - the set itself must not be null, but null is an acceptable type within the set and indicates the EventList expects to contain null elements
        Returns:
        the ListEventListener providing the safety checking on the given source. To stop the type safety checking, use EventList.removeListEventListener(ListEventListener).

      • syncEventListToMultiMap

        public static <K extends java.lang.Comparable,​V> DisposableMap<K,​java.util.List<V>> syncEventListToMultiMap​(EventList<V> source,
                                                                                                                        FunctionList.Function<V,​? extends K> keyMaker)
        Synchronize the specified EventList to a MultiMap that is returned from this method. Each time the EventList is changed the MultiMap is updated to reflect the change.

        This can be useful when it is known that an EventList will experience very few mutations compared to read operation and wants to provide a data structure that guarantees fast O(1) reads.

        The keys of the MultiMap are determined by evaluating each source element with the keyMaker function. This form of the MultiMap requires that the keys produced by the keyMaker are Comparable and that the natural ordering of those keys also defines the grouping of values. If either of those assumptions are false, consider using syncEventListToMultiMap(EventList, FunctionList.Function, Comparator).

        If two distinct values, say v1 and v2 each produce a common key, k, when they are evaluated by the keyMaker function, then a corresponding entry in the MultiMap will resemble:

        k -> {v1, v2}

        For example, assume the keyMaker function returns the first letter of a name and the source EventList contains the names:

        {"Andy", "Arthur", "Jesse", "Holger", "James"}

        The MultiMap returned by this method would thus resemble:

        "A" -> {"Andy", "Arthur"}
        "H" -> {"Holger"}
        "J" -> {"Jesse", "James"}

        It is important to note that all mutating methods on the Map interface "write through" to the backing EventList as expected. These mutating methods include:

        • the mutating methods of Map.keySet() and its Iterator
        • the mutating methods of Map.values() and its Iterator
        • the mutating methods of Map.entrySet() and its Iterator
        • the Map.Entry.setValue(V) method
        • the mutating methods of Map itself, including Map.put(K, V), Map.putAll(java.util.Map<? extends K, ? extends V>), Map.remove(java.lang.Object), and Map.clear()
        For information on MultiMaps go here.
        Parameters:
        source - the EventList which provides the master view. Each change to this EventList will be applied to the MultiMap
        keyMaker - the FunctionList.Function which produces a key for each value in the source. It is imperative that the keyMaker produce immutable objects.
        Returns:
        a MultiMap which remains in sync with changes that occur to the underlying source EventList

      • syncEventListToMultiMap

        public static <K,​V> DisposableMap<K,​java.util.List<V>> syncEventListToMultiMap​(EventList<V> source,
                                                                                           FunctionList.Function<V,​? extends K> keyMaker,
                                                                                           java.util.Comparator<? super K> keyGrouper)
        Synchronize the specified EventList to a MultiMap that is returned from this method. Each time the EventList is changed the MultiMap is updated to reflect the change.

        This can be useful when it is known that an EventList will experience very few mutations compared to read operation and wants to provide a data structure that guarantees fast O(1) reads.

        The keys of the MultiMap are determined by evaluating each source element with the keyMaker function. This form of the MultiMap makes no assumptions about the keys of the MultiMap and relies on the given keyGrouper to define the grouping of values.

        If two distinct values, say v1 and v2 each produce a common key, k, when they are evaluated by the keyMaker function, then a corresponding entry in the MultiMap will resemble:

        k -> {v1, v2}

        For example, assume the keyMaker function returns the first letter of a name and the source EventList contains the names:

        {"Andy", "Arthur", "Jesse", "Holger", "James"}

        The MultiMap returned by this method would thus resemble:

        "A" -> {"Andy", "Arthur"}
        "H" -> {"Holger"}
        "J" -> {"Jesse", "James"}

        It is important to note that all mutating methods on the Map interface "write through" to the backing EventList as expected. These mutating methods include:

        • the mutating methods of Map.keySet() and its Iterator
        • the mutating methods of Map.values() and its Iterator
        • the mutating methods of Map.entrySet() and its Iterator
        • the Map.Entry.setValue(V) method
        • the mutating methods of Map itself, including Map.put(K, V), Map.putAll(java.util.Map<? extends K, ? extends V>), Map.remove(java.lang.Object), and Map.clear()
        For information on MultiMaps go here.
        Parameters:
        source - the EventList which provides the master view. Each change to this EventList will be applied to the MultiMap
        keyMaker - the FunctionList.Function which produces a key for each value in the source. It is imperative that the keyMaker produce immutable objects.
        keyGrouper - the Comparator which groups together values that share common keys
        Returns:
        a MultiMap which remains in sync with changes that occur to the underlying source EventList

      • syncEventListToMap

        public static <K,​V> DisposableMap<K,​V> syncEventListToMap​(EventList<V> source,
                                                                      FunctionList.Function<V,​K> keyMaker)
        Synchronize the specified EventList to a Map that is returned from this method. Each time the EventList is changed the Map is updated to reflect the change.

        This can be useful when it is known that an EventList will experience very few mutations compared to read operation and wants to provide a data structure that guarantees fast O(1) reads.

        The keys of the Map are determined by evaluating each source element with the keyMaker function. The Map implementation assumes that each value has a unique key, and verifies this invariant at runtime, throwing a RuntimeException if it is ever violated. For example, if two distinct values, say v1 and v2 each produce the key k when they are evaluated by the keyMaker function, an IllegalStateException is thrown to proactively indicate the error.

        As for example of normal usage, assume the keyMaker function returns the first letter of a name and the source EventList contains the names:

        {"Kevin", "Jesse", "Holger"}

        The Map returned by this method would thus resemble:

        "K" -> "Kevin"
        "J" -> "Jesse"
        "H" -> "Holger"

        It is important to note that all mutating methods on the Map interface "write through" to the backing EventList as expected. These mutating methods include:

        • the mutating methods of Map.keySet() and its Iterator
        • the mutating methods of Map.values() and its Iterator
        • the mutating methods of Map.entrySet() and its Iterator
        • the Map.Entry.setValue(V) method
        Parameters:
        source - the EventList which provides the values of the map. Each change to this EventList will be applied to the Map.
        keyMaker - the FunctionList.Function which produces a key for each value in the source. It is imperative that the keyMaker produce immutable objects.
        Returns:
        a Map which remains in sync with changes that occur to the underlying source EventList