编译Java程序时遇到问题，我是新手。 无法弄清楚如何处理目录

Question

I have been searching the web trying to find the answer to my question, but everywhere I look seems to have too complex of a solution for a beginner like me. I have been working on this project, and just now realized that I should've made a package, or something like that. The thing is though, my program was working fine until I started dabbling with it, and now it won't work at all. I am getting this error:

Exception in thread "main" java.lang.NoClassDefFoundError: BubbleSort. class
Caused by: java.lang.ClassNotFoundException: BubbleSort.class
        at java.net.URLClassLoader.findClass(URLClassLoader.java:434)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:672)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:358)
        at ``java.lang.ClassLoader.loadClass(ClassLoader.java:638)
Could not find the main class: BubbleSort.class.  Program will exit.

Here's how my "path" looks, if I am not mistaken. I am connected to my school's Z: drive through a remote connection, and from there I have a folder called myFirstname_Lastname_A4, which then leads me to another folder called sortingzz which I believe is supposed to have only my source files, but it also ended up with my class files in there whenever I compiled. So here's what I am doing to compile.

 cd myFirstname_Lastname_A4/sortingzz

javac *.java (Works fine, this is where I end up with my Class files inside of my sortingzz folder)

java * (This is where I get the error)

I am pretty sure I am just trying to run the program wrong. Before I started messing around with stuff I wasn't ready for, I used to just run the file with my main function in it, like this

javac SortingImplementation.java

java SortingImplementation

And that for the most part worked fine, but I started having trouble calling certain classes from other classes, so thats when I found out I was suppose to do the packaging and importing stuff.

In case that is the issue, I have on the top line of every source file: package sortingzz;

and I am importing like this:

import sortingzz.* ;

This is correct, right?

UPDATE:

I decided to give up on class pathing and trying to package everything, because as usual, I am getting responses that are way over my head, and to be honest I don't think it is necessary.

After removing package and importing from everything, and once again compiling using javac *., it actually compiles this time. However whenever I try to run my class with the main in it, SortingImplementation, it tells me that

Could not find the main class: SortingImplementation.  Program will exit.

I don't get it, I am looking at the SortingImplementation.class right now, with all the other classes and java files, so I am not sure what it's trying to do.

Answer 1

javac *.java is fine. This will compile your files. However, you only need to run the file with your main method in it: java MainClass

Answer 2

You say that you are using packages to organize the classes. In this case you need to set the class path using the -cp flag.

javac -cp /path/to/parent/of/package classname.java
and
java classname

Also, your main class should be declared public and should have a main()

Answer 3

NoClassDefFoundError occures when a class was recognised in compile time but was not available during runtime. So the JVM can't find your class in the classpath.

using -cp flag to specify where your package is should work.

Answer 4

the commanc javac *.java compiles all found java files to corresponding .class files. If you all your classfiles are in the same folder, which they should, you just run your regular java SortingImplementation command.

java * would, a bit depending on your OS, yield in an undesired command. For instance, on Linux it would be expanded by the OS to java SortingImplementation.java SortingImplementation.class BubbleSort . The last one is a directory, which ofcourse is not an executable class.