To add to farrell2k's suggestion, as I think he's on the right track: If you copy the files from their original folder into the Eclipse file structure - into the workspace/project/src folder - you may not see the changes right away in Eclipse. To show what you've done in Eclipse, select your project and depress F5, or right click on your project and select "Refresh." After doing that, the files you copied into the src folder should appear. As farrell2k also suggested, if your existing source files have package declarations, Eclipse may move them into the correct src/package folders when you "Refresh" Eclipse, or you may be shown an error message that the files are not in the correct location, offering to move them for you. I forget which you'll see.
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Create a project in Eclipse. Take the .java files from your src folder and just copy them into eclipse. You may have to change package declarations in the .java files.
Won't work, they will not be recognized as being part of the project
You will have to:
- create the project as mentionned
- use Eclipse File... Import ... File System to bring (and be registered) your files into the project