Why can't the main class be found after copying and pasting the package in IDEA? Is there any solution?

Can't find the main class after copying and pasting the package in IntelliJ IDEA? Detailed solution explanation

When IntelliJ IDEA is doing Java development, it is a common problem not to find the main class after copying and pasting the package. Strangely, the program can run normally by copying the package directly to the src directory of the project folder. This is due to the difference between IDEA's internal project model and file system operations.

IDEA maintains an internal project model of information such as project structure, dependencies and class indexes. Copying and pasting packages in the IDEA interface is actually done through the IDEA file system. Although the physical location of the file has changed, IDEA's internal model may not be updated in time, resulting in the unrecognition of newly added classes.

Directly operating files on disk bypasses IDEA's internal file system. Although the file is in the correct location, IDEA still needs to reload the file to update its internal model.

The following methods can help IDEA re-identify files:

1. Reload the project: Right-click on the project root directory, select "Reload Project from Disk", and force IDEA to reload the project structure.

2. Refresh the project: Right-click on the project's src directory, select "Refresh" to update the index of IDEA to the directory.

3. Rebuild the project: Select "Build" -> "Rebuild Project", force IDEA to recompile all files and update the index.

Through the above operations, IDEA can re-identify newly added packages and classes to solve the problem of "main class not found". Understanding IDEA's internal working mechanism can better deal with similar problems.

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