How to run a java class on ubuntu?

Question

If I compile and run the program. I don't have any issues.

public class HelloWorld {
    public static void main(String[] args) {
        // Prints "Hello, World" to the terminal window.
        System.out.println("Hello, World");
    }
}

If I add the line package ch01.sec01; it complies correctly with javac. However when I try to run it using java I get:

Error: Could not find or load main class HelloWorld

I have tried the following.

export CLASSPATH=/usr/lib/jvm/java-9-openjdk-amd64/bin:/usr/lib/jvm/java-1.9.0-openjdk-amd64/bin

We'll need the complete command line you used. Your classname is not HelloWorld it's ch01.sec01.HelloWorld. — markspace
– markspace, Commented Jan 25, 2018 at 23:58
When you have a package ch01.sec01 the class file is written to cg01/sec01/.... You must use the full name. — Thorbjørn Ravn Andersen
– Thorbjørn Ravn Andersen, Commented Jan 26, 2018 at 0:24

kyriakosSt · Accepted Answer · 2018-01-26 00:01:26Z

2

That is why when you use a package in your code, that path must be the actual path of your java file (That means that your code is supposed to be in a directory called sec01 which is inside directory ch01).
With that being set, when running code inside a package, you need to include the path in the command. To do so, after you have compiled your code with javac, navigate to the root of the path (outside ch01 directory) and type

java ch01.sec01.HelloWorld

This should work.

answered Jan 26, 2018 at 0:01

kyriakosSt

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