I added a Java project (containing one default package with 2 classes) to my folder which I declare as my workspace in Eclipse. But when I launch Eclipse, it does not add this project in the package explorer. What can I do to solve this problem?
You can't copy files or folders to your workspace folder, you have to import the project into Eclipse:
File > Import....
The Import wizard opens.General > Existing Project into Workspace
and click Next.Select root directory
or Select archive file
and click the associated Browse to locate the directory or file containing the projects.