How to fix "ClassNotFoundException" error while running Java program

I am learning Java and trying to run a simple Java program using the command prompt. I created a basic program to print a message, and the program compiles successfully using the javac command. However, when I try to run the program using the java command, I get an error saying "Error: Could not find or load main class" or sometimes ClassNotFoundException.
Example code:
Java
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public class HelloWorld {
   public static void main(String[] args) {
       System.out.println("Hello World");
   }
}
Commands I used:
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javac HelloWorld.java
java HelloWorld
The program compiles without any errors, but when I try to run it, the system cannot find the main class.
I would like to know:
Why this error occurs even though the program compiles successfully.
Whether it is related to the classpath or folder location.
The correct way to compile and run a Java program from the command line.
Please explain the reason and provide the correct steps to resolve this issue.

That is how you would usually run a Hello World program. Please try one‑file execution:-java HelloWorld.javaYou may be right about classpath problems. Please show us your classpath because that is a likely cause of your problem.

I have just tried it on my computer and it works fine with the command:java HelloWorldAre you sure the file HelloWorld.class has been created?

OP did say the compiler ran normally.

You are right. I only did not know what else to check.

This also may be caused by wrong value in the CLASSPATH environment variable.
I would tryjava -cp . HelloWorld