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This application consists of three separate source files located in three different packages. Together they illustrates the use ofpackage and import directives, along with javac to build a standalone Java application consisting of classes in three separatepackages.
(If you want to confirm that they are really in different packages, just make one of the classes referred to by the controlling classnon-public and try to compile the program.)
In other words, in this sample program, we create our own package structure and populate it with a set of cooperating class files.
A folder named jnk is a child of the root folder on the M-drive.
A folder named SampleCode is a child of the folder named jnk .
A folder named Combined is a child of the folder named SampleCode .
A folder named Java is a child of the folder named Combined .
Folders named p1 and p2 are children of the folder named Java .
The file named Package00.java , shown in Listing 1 is stored in the folder named Java .
| Listing 1 . File: Package00.java. |
|---|
/*File Package00.java Copyright 1997, R.G.Baldwin
Illustrates use of package and import directives tobuild an application consisting of classes in three
separate packages.The output from running the program follows:Starting Package00
Instantiate obj of public classes in different packagesConstructing Package01 object in folder p1
Constructing Package02 object in folder p2Back in main of Package00
**********************************************************/package Combined.Java; //package directive
//Two import directivesimport Combined.Java.p1.Package01;//specific form
import Combined.Java.p2.*; //wildcard formclass Package00{
public static void main(String[]args){ //main method
System.out.println("Starting Package00");System.out.println("Instantiate obj of public " +"classes in different packages");
new Package01();//Instantiate objects of two classesnew Package02();// in different packages.
System.out.println("Back in main of Package00");}//end main method}//End Package00 class definition. |
The file named Package01.java , shown in Listing 2 is stored in the folder named p1 .
| Listing 2 . File Package01.java. |
|---|
/*File Package01.java Copyright 1997, R.G.Baldwin
See discussion in file Package00.java**********************************************************/
package Combined.Java.p1;public class Package01 {
public Package01(){//constructorSystem.out.println(
"Constructing Package01 object in folder p1");}//end constructor
}//End Package01 class definition. |
The file named Package02.java , shown in Listing 3 is stored in the folder named p2 .
| Listing 3 . File Package02.java. |
|---|
/*File Package02.java Copyright 1997, R.G.Baldwin
See discussion in file Package00.java**********************************************************/
package Combined.Java.p2;public class Package02 {
public Package02(){//constructorSystem.out.println(
"Constructing Package02 object in folder p2");}//end constructor
}//End Package02 class definition. |
The file named CompileAndRun .bat, shown in Listing 4 is stored in the folder named SampleCode .
| Listing 4 . File: CompileAndRun.bat. |
|---|
echo off
rem This file is located in folder named M:\SampleCode,rem which is Parent of folder Combined.
del Combined\Java\*.classdel Combined\Java\p1\*.class
del Combined\Java\p2\*.classjavac -cp M:\jnk\SampleCode Combined\Java\Package00.java
java -cp M:\jnk\SampleCode Combined.Java.Package00pause |
The controlling class named Package00 is stored in the package named Combined.Java , as declared in Listing 1 .
The class named Package01 is stored in the package named Combined.Java.p1 , as declared in Listing 2 .
The class named Package02 is stored in the package named Combined.Java.p2 , as declared in Listing 3 .
The controlling class named Package00 imports Combined.Java.p1.Package01 and Combined.Java.p2.* , as declared in Listing 1 .
Code in the main method of the controlling class in Listing 1 instantiates objects of the other two classes in different packages. Theconstructors for those two classes announce that they are being constructed.
The two classes being instantiated are public . Otherwise, it would not be possible to instantiate them from outside their respectivepackages.
This program was tested using JDK 7 under Windows by executing the batch file named CompileAndRun.bat .
The classpath is set to the parent folder of the folder named Combined (M:\jnk\SampleCode) by the -cp switch in the file named CompileAndRun.bat .
The output from running the program is shown in the comments at the beginning of Listing 1 .
I encourage you to copy the code from Listing1 through Listing 4 into a properly constructed tree of folders. Compile the code and executeit. Experiment with the code, making changes, and observing the results of your changes. Make certain that youcan explain why your changes behave as they do.
As you approach the end of this group of Programming Fundamentals modules, you should be preparing yourself for the more challenging ITSE 2321 OOPtracks identified below:
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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