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Not difficult to demonstrate

Although this is not demonstrated by this program, it is easy to modify the program to demonstrate this feature.

A String representation of the array object can be displayed using a System.out.println(array) statement before and after the array is passed to the toArray method.

Array as large as or larger than collection

For the cases where my array contained six, seven, or eight elements, and the collection contained six elements, the String representations of the array object before and after the call to the toArray method were the same. For one case, those String representations were as follows:

[Ljavax.swing.JComponent;@49ba38 [Ljavax.swing.JComponent;@49ba38

In other words, the reference variable named array referred to the same array object before and after the call to the toArray method.

Array smaller than the collection

When I reduced the size of the array to five elements, keeping the size of the collection at six elements, the before and after String representations of the array object were as follows:

[Ljavax.swing.JComponent;@506411 [Ljavax.swing.JComponent;@21807c

In this case, the reference to the array object returned by the toArray method was different from the reference that was passed to the toArray method. In other words, the returned reference referred to a different arrayobject than was referred to by the reference that was passed to the toArray method.

Modify an object

As in the program in the previous module, the code shown in Listing 6 modifies the value of the toolTipText property of the object whose reference is stored in index 0 of the array.

Listing 6 . Modify an object .
((JComponent)array[0]).setToolTipText("XX");showArray(array,"Modified array contents"); showCollection(ref,"Collection contents");

The code in Listing 6 also displays the contents of the array and the contents of the collection after the modification is made.

The output produced by the code in Listing 6 is shown below:

Modified array contents XX B1 L2 B3 B4 L5 null 17Collection contents XX B1 L2 B3 B4 L5

Now for the caution

Note that the value of the toolTipText property of the object referred to by the reference at index 0 of the array, and the same property of the objectreferred to by the reference at index 0 of the collection was overwritten by "XX". (This is true because both references refer to the same object.)

This is the case regardless of which version of the toArray method is used. Therefore, the same cautions discussed in the previous module apply hereas well.

Run the program

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.

Summary

In this module, I taught you how to use the more-complex version of the two overloaded versions of the toArray method, declared in the Collection interface, to copy the elements from a collection into an array of type JComponent .

I discussed issues regarding the type of the array and the type of the objects referred to by the elements in the container. I also discussed issuesregarding the size of the array as compared to the number of elements in the collection.

Finally, I reaffirmed that you need to exercise care when using the elements stored in the array, to avoid corrupting the state of the objects referred to bythe elements in the collection.

What's next?

For now, at least, this module concludes the series of modules on the Java Collections Framework. If I have time later, I will come back and add moremodules to teach you how to use the Map and SortedMap interfaces, and the concrete class implementations of those interfaces.

Miscellaneous

This section contains a variety of miscellaneous information.

Housekeeping material
  • Module name: Java4160: The toArray Method, Part 2
  • File: Java4160.htm
  • Published: 05/07/13
Disclaimers:

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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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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