_ is not on the classpath of project _, only syntax errors are reported

Every time I try to create a package for my java classes so I can finish my projects for school, errors like this occur:

When I finally try to run the program, I get an even more infuriating message:

It hurts me to be unable to properly test my code, even if I know I did well. It has been giving me anxiety for quite a while now, so I'm quite surprised this has slipped under the radar for so long.

• Operating System:
  

• JDK version: 15.0.2

• Visual Studio Code version:
  

• Java extension version:
  
  

Steps To Reproduce

1. Create a java class with methods and everything.
2. Put it in a folder with a test program.
3. List the folder as a package in both programs.
4. Try to use the class and it's methods in the test program. Both errors should be clearly visible by now.

Here is my code as an example of what can cause it. Try compiling either Test.java or Customer.java and it should be quite apparent.
Chapter10.zip

Current Result

A warning that constantly results in weird compiler errors

Expected Result

A working class that I can use

首先打开附加的 Chapter10.zip，并使用 JDK 15.0.2 在 VS Code 中通过 Test.java 和 Customer.java 复现该报告。检查 Java 扩展对 package 和 classpath 设置的处理方式。完成的标准是 classpath 警告得到解决，并且示例类能够按预期编译和运行。