Why am I getting this error in eclipse involving initialization of boot layer?

问题

I am trying to set up my eclipse environment for the sedgewick algorithms course and I keep receiving the following error:

Error occurred during initialization of boot layer
java.lang.module.FindException: Unable to derive module descriptor for /home/yannik/algs4/algs4.jar
Caused by: java.lang.module.InvalidModuleDescriptorException: TestAlgs4.class found in top-level directory (unnamed package not allowed in module)

Why is this happening and how do I fix this?

And the image is attached. I created a class Rational under the default package in source.

来源：https://stackoverflow.com/questions/63877831/why-am-i-getting-this-error-in-eclipse-involving-initialization-of-boot-layer