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In this module, I have provided a brief introduction to the use of the Java Collections Framework . The framework is designed to encourage you to reuse rather than to reinvent collections and maps (I will have more to say about maps in a future module).
A collection represents a group of objects, known as its elements.
While some collections allow duplicate elements, others do not. Some collections are ordered and others are not ordered.
The Collections Framework is defined by a set of interfaces and associated contracts. The framework provides concrete implementations of the interfaces (classes) for the most common data structures. In addition, the framework also provides several abstract implementations, which are designed to make iteasier for you to create new and different concrete implementations.
The TreeSet class is a concrete implementation of the SortedSet interface. The SortedSet interface extends Set , which extends Collection . Thus, a TreeSet object is a SortedSet . Also it is a Set , and it is a Collection .
The TreeSet class guarantees that the sorted set will be in ascending element order, and provides guaranteed log(n) time cost for the basic operations( add , remove and contains ).
TreeSet objects can be treated as the generic type Collection . Methods declared in the Collection interface can be called on a Collection object without regard for the actual class from which the object wasinstantiated. (This is polymorphic behavior.)
When such methods are called, the author of the program can have confidence that the behavior of the method will be appropriate for an object of the class from which the object was instantiated. In my opinion, this is thetrue essence of object-oriented behavior.
This is the first module in a miniseries on the Collection Framework . Subsequent modules will teach you how to use the framework for creating andusing various types of collections and maps.
Once you learn how to use the framework, it is unlikely that you will need to reinvent classical data structures, search algorithms, or sorting algorithms,because those capabilities are neatly packaged within the framework.
This section contains a variety of miscellaneous information.
Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.
I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.
In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.
Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.
A complete listing of the program is provided in Listing 6 below.
| Listing 6 . Complete program listing. |
|---|
import java.util.TreeSet;
import java.util.Collection;import java.util.Iterator;
public class AP400{public static void main(
String args[]){
new Worker().doIt();}//end main()
}//end class AP400class Worker{
public void doIt(){Collection ref = new TreeSet();
Populator.fillIt(ref);Iterator iter = ref.iterator();
while(iter.hasNext()){System.out.print(iter.next());
}//end while loopSystem.out.println();
}//end doIt()}// end class Worker
class Populator{public static void fillIt(
Collection ref){ref.add(new Integer(4));
ref.add(new Integer(4));ref.add(new Integer(3));
ref.add(new Integer(2));ref.add(new Integer(1));
}//end fillIt()}//end class populator |
-end-
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