Just delete module-info.java at your Project Explorer tab.
The "delete module-info.java at your Project Explorer tab" answer is the easiest and most straightforward answer, but
for those who would want a little more understanding or control of what's happening, the following alternate methods may be desirable;
Reason of the error: Package name left blank while creating a class. This make use of default package. Thus causes this error.
helloWorld.javafile in that package. Just drag and drop on the package. Error should disappear.
Latest version of Eclipse required java11 or above. The
module feature is introduced in java9 and onward. It was proposed in 2005 for Java7 but later suspended. Java is object oriented based. And module is the moduler approach which can be seen in language like C. It was harder to implement it, due to which it took long time for the release. Source: Understanding Java 9 Modules
When you create a new project in Eclipse then by default module feature is selected. And in Eclipse-2020-09-R, a pop-up appears which ask for creation of
module-info.java file. If you select
don't create then
module-info.java will not create and your project will free from this issue.
Best practice is while crating project, after giving project name. Click on
next button instead of
finish. On next page at the bottom it ask for creation of
module-info.java file. Select or deselect as per need.
If selected: (by default) click on
finish button and give name for module. Now while creating a class don't forget to give package name. Whenever you create a class just give package name. Any name, just don't left it blank.
If deselect: No issue