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This chapter covers entire ninth SCJP objective. We learned about the six core interfaces of java collection framework. We also learned the three types of collections, lists, sets and maps and the difference between them. We then quickly overviewed some implementations of these interfaces and significant facts about each implementation. Finally we learned the overriding the equals() and hashCode() method and its significance for collection classes. Here is a brief summary of the important concepts learned in this chapter.
Collections
§ Common collection activities include
§ Adding objects, removing objects.
§ Searching and retrieving objects
§ Iterating over collection.
§ Three context in which the word ‘collection’ is used
§ collection—Represents the data structure in which objects are stored
§ Collection—java.util.Collection—Interface from which Set and List extend
§ Collections—A class that holds static collection utility methods
Three basic flavors of collections include Lists, Sets, Maps:
Lists of things:
§ Ordered
§ duplicates are allowed, with an index
Sets of things:
§ May or may not be ordered and/or sorted
§ duplicates not allowed
Maps of things with keys:
§ May or may not be ordered and/or sorted,
§ duplicate keys not allowed
.Four basic subflavors of collections include- Sorted, Unsorted,
Ordered, Unordered.
§ Ordered means iterating through a collection in a specific, nonrandom order.
§ Sorted means iterating through a collection in a natural [*********]sorted order.
Key attributes of common collection classes:
§ ArrayList: Fast iteration and fast random access
§ Vector: Like a somewhat slower ArrayList, mainly due to its synchronized methods
§ LinkedList: Good for adding elements to the ends, i.e., stacks and queues
§ HashSet: Assures no duplicates, provides no ordering
§ LinkedHashSet: No duplicates; iterates by insertion order or last accessed (new with 1.4)
§ TreeSet: No duplicates; iterates in natural sorted order
§ HashMap: Fastest updates (key/value pairs); allows one null key, many null values
§ Hashtable: Like a slower HashMap (as with Vector, due to its synchronized methods). No null values or null keys allowed
§ LinkedHashMap: Faster iterations; iterates by insertion order or last accessed, allows one null key, many null values (new with 1.4)
§ TreeMap: A sorted map, in natural order