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Listing 11 shows the class from which the Comparator object was instantiated.
This is essentially the same class that was used to instantiate a Comparator object in an earlier module. I discussed the compare method in detail in that module and won't repeat that discussion here.
| Listing 11 . The class named TheComparator. |
|---|
class TheComparator implements Comparator,Serializable{
public int compare(Object o1,Object o2){if(!(o1 instanceof String))
throw new ClassCastException();if(!(o2 instanceof String))
throw new ClassCastException();int result = ((String)o1).compareTo(((String)o2));
return result*(-1);}//end compare()
}//end class TheComparator |
Suffice it to say at this point that this Comparator object causes the elements in the array to be sorted into reverse natural order . That term was also explained in the previous module, so I won't discuss it further here.
The code in Listing 12 was used to display the newly-sorted contents of the array.
| Listing 12 . Display the contents again. |
|---|
System.out.println("Custom order sorted " +
"array data");display(array); |
The output produced by this code is:
Custom order sorted array data
Tom TOM Joe JOE Bill BILL You will recognize this as reverse natural order for the elements contained in the array.
It is important to note that I could have caused the sorting order to be different from reverse natural order simply by defining the rules used for comparison in the compare method shown in Listing 11 above. This makes it possible for you to sort array data into any order that you choose aslong as you can write the sorting rules into the compare method of a class that implements the Comparator interface.
Finally, in order to show that none of this has disturbed the contents of the original collection, the code in Listing 13 gets and uses an iterator to display the contents of the Vector collection.
| Listing 13 . Display the collection data again. |
|---|
iter = ref.iterator();
System.out.println("Collection data");while(iter.hasNext()){
System.out.print(iter.next() + " ");}//end while loop |
The output produced by the code in Listing 13 is:
Collection data
Joe Bill Tom JOE BILL TOM If you compare this with the output produced by the code at the beginning of the program, you will see that the iterator still returns the elements in the Vector in the same order that they were added. Thus, modifications to the array did not disturb the contents of the Vector collection.
The toArray method of the Collection interface makes it possible to extract a copy of the elements in a collection into an array and tomanipulate those elements in whatever way you wish. As mentioned earlier, however, care should be exercised to make certain that the copies of thereferences to the original objects are not used to corrupt the objects.
The various versions of the sort method in the Arrays class make it possible to sort the contents of arrays in a variety of different ways.
I encourage you to copy the code from Listing 1 . Paste the code into your Java editor. 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.
In this module, I taught you how to extract the contents of a collection into an array and how to use a Comparator to sort the contents of the array into reverse natural order .
Although I elected to use reverse natural order for purposes of illustration, I could have sorted the array into some other order simply bydefining the comparison rules in the compare method of the Comparator class differently.
In order to further expand your knowledge of array sorting, I also sorted the array into natural order without the use of a Comparator .
Sorting the contents of the array did not disturb the contents of the Vector collection from which the contents of the array were derived.
In the next module, I will show you how to use the sort method of the Collections class along with a Comparator object to sort the contents of a List .
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.
-end-
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