Cannot run ajc compiled class file in the terminal using Java

I trying to learn aspectj for a project. I wish to run the java files from the terminal using ajc and java but I am unable to do so.

I have 2 files in my directory HelloWorld.java and HWTracer.aj

Contents of Helloworld.java

public class HelloWorld {

  public static void main(String[] args) {
    printMsg("Hello, World!!");
  }

  public static void printMsg(String msg) {
    System.out.println("\n");
    System.out.println("    " + msg);
    System.out.println("\n");
  }
}

Contents of HWTracer.aj

public aspect HWTracer {
    // pointcuts
    pointcut theMainMethod() : execution(public static void main(String[]));
    pointcut theCall() : call (* HelloWorld.printMsg(*));

    // advice
    before(): theMainMethod() {
        System.out.println("Before the Main");
    }

    // note this is after main is done, after the entire program finishes
    after(): theMainMethod() {
        System.out.println("After the Main");
    }  

    before(): theCall() {
        System.out.println("-- before the call --");
    }

    after(): theCall() {
        System.out.println("-- after the call --");
    }
}

Here is the command I use to compile the code

ajc .\HelloWorld.java .\HWTracer.aj -cp C:\aspectj1.9\lib\aspectjrt.jar;C:\aspectj1.9\lib\aspectjtools.jar;C:\aspectj1.9\lib\aspectjweaver.jar

I run the compiled file using the following command:

java -cp C:\aspectj1.9\lib\aspectjrt.jar HelloWorld HWTracer

And I get the following error:

Exception in thread "main" java.lang.NoClassDefFoundError: org/aspectj/lang/NoAspectBoundException
    at HelloWorld.main(HelloWorld.java:5)

Please note that I am by no means a java expert.

Solution

On the compilation classpath, aspectjrt should be enough, just like on the runtime one.

On the runtime classpath, you need to add the directory your compiled classfiles reside in, in your case obviously just the current directory ".":

xxx> ajc -cp "lib\aspectjrt.jar" HelloWorld.java HWTracer.aj

xxx> java -cp ".;lib\aspectjrt.jar" HelloWorld

Before the Main
-- before the call --


    Hello, World!!


-- after the call --
After the Main

Also note that when running the main class, there is no need to mention the aspect class separately. Java would interpret it as a command line parameter to the main class.

Please do learn some Java basics first, before you try to understand a complex tool like AspectJ. If you do not even know how to correctly run a Java program from the command line, maybe the time is not right yet to take the second step. Buildings without solid foundations tend to be shaky.