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How do I compile and run the following programs:

Test1.java:

package A; public class Test1 { public int a = 1; }

Test2.java:

package B; import A.*; public class Test2 { public static void main(String [] args) { Test1 obj = new Test1(); System.out.println(obj.a); } }

I'm new to packages. If I compile using javac *.java and manually create dir A, copy Test1.class into it and manually create dir B and copy Test2.class into it and then run java B.Test2 it works. I'm sure this is not the right way of doing it. Please suggest.

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  • Some suggested the use of IDEs, but I am trying to understand what exactly happens under the hood. Some mentioned Ant/Maven. What is the difference? I know how make works. I guess these are similar to make. Which one should I start with, Ant or Maven? Commented Jan 29, 2010 at 3:36

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You need to keep your java files in the correct directory structure:

A/Test1.java B/Test2.java

It's usually sufficient to only invoke javac on your main class, as all dependencies will be handled automatically. After I say javac B/Test2.java, it looks like this:

A/Test1.class A/Test1.java B/Test2.class B/Test2.java

And I can run the program with java B.Test2.

If it's not enough just to run javac on your main class, you'll probably need a build system.

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2

you should keep your .java files in directory structure matching your package structure

so Test1.java should go in directory A so Test2.java should go in directory B

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Thanks objects, it works :) But now I need to use javac twice !! Is there a way to issue a single javac command ?
once you start creating apps that are > 1 class you're better off using something like ant or maven to do your compiling. you can also list many files to compile eg. java A/*.java B/*.java Or you can just compile Test2.java and Test1 will be compiled (if not already) as it is used by Test2
"you're better off using something like ant or maven to do your compiling". Or an IDE like Eclipse or Netbeans. They also make the coding itself much easier.
I would recommend to first grasp the compile process, packages, the classpath and all that works. Then familiarize with an IDE and then take on a tool like ant or maven.
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There's nothing wrong with the way you are compiling, it's just cumbersome but certainly not wrong.

That being said, create a src directory to store your .java files, keeping your directory structure coherent with the package structure of your classes. In this case you would have src directory and inside it, directory A and directory B. Inside A put Test1.java and inside B put Test2.java

Then:

javac B/Test2.java

Why Test2.java? Because it depends on A, then the compiler is smart enough to first compile A/Test1.java and then B/Test2.java. At this point you have each .class files inside A and B

To run it:

java B.Test2
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The compiler will create directories called A and B and place the .class files within them.

You should not need to copy the class files manually into their package directories, and it will probably not work if you do that.

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This isn't a direct answer to your question but you might want to start thinking about using an IDE (others suggested ant). I would recommend jcreator if you are just starting out or Eclipse if you want something good.

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