4.6 Java4040: purpose of framework implementations and algorithms  (Page 6/6)

Drive home the point

I placed this question here to drive home the point that the methods declared in the Collection interface can be called on collection objects in a polymorphic manner.

That is to say, as a user of an object instantiated from a class that properly implements the Collection interface (according to the contracts of the Collections Framework) , you can call the methods declared in that interface on a reference to the object and be confident thatthe actual method that is called will be the version that is appropriate for the class from which the object was instantiated. This is polymorphic behavior.

In the event that you need to call a method that is not declared in the Collection interface (such as the get() method in Listing 4 above), you can pass the reference as one of the more specialized sub-interfaces of Collection , such as Set .

(Author's note: Once again, this document was originally written before the release of Generics. The use of the more specializedsub-interfaces described above may not be required if the program is re-written making proper use of Generics.)

Benefits of using the Collections Framework

The Java Tutorial from Oracle lists and explains the benefits of using the Java Collections Framework, including the following.

• It reduces programming effort
• It increases program speed and quality
• It allows interoperability among unrelated APIs
• It reduces the effort to learn and use new APIs
• It reduces effort to design new APIs
• It fosters software reuse

For a detailed explanation of these benefits, I am simply going to refer you directly to The Java Tutorial .

Run the program

I encourage you to copy the code from Listing 1 and paste it into a Java source code file. Thencompile and execute it.

Run the program and observe the results. Experiment with the code. Make changes, run the program again, and observe the results of your changes. Make certain that youcan explain why your changes behave as they do.

Summary

Let's recap some of what we have learned in this and the previousmodules.

The core collection interfaces in the Collections Framework are shown below.

• Collection
  • Set
    • SortedSet
  • List
  • Queue
  • Deque
• Map
  • SortedMap

The basic purpose of the core collection interfaces in the Java Collections Framework is to allow collections to be manipulated without regard for how thecollections are implemented, provided of course that the implementations comply with the contracts.

The framework provides at least the following nine concrete implementations (classes) of the interfaces shown above:

• HashSet
• TreeSet
• LinkedList
• ArrayList
• Vector
• HashMap
• WeakHashMap
• TreeMap
• Hashtable

For example, the classes TreeSet and ArrayList are concrete implementations of the Collection interface as shown in the above list.

(Actually, they are concrete implementations of sub-interfaces of Collection. The Collections Framework doesn't provide any direct implementations of the Collectioninterface.)

A collection object instantiated from the class TreeSet and a collection object instantiated from the class ArrayList can each be viewed as being of the interface type Collection .

Methods having the same signatures can be used to manipulate either collection with confidence that the behavior of the method will be appropriatefor the actual type of collection involved.

The framework also provides the following incomplete implementations of the core interfaces:

• AbstractSet
• AbstractList
• AbstractMap

The purpose of these implementations is to provide you with a starting point for defining your own concrete implementations for more specialized collections.

Miscellaneous

This section contains a variety of miscellaneous information.

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