IntelliJ IDEA and Eclipse store project information including information on external modules in different places and using different file formats---mostly different XML schemas. You have .classpath and .project files in Eclipse; you have a .iml file in IntelliJ IDEA.
How can you share the same project across two distinct IDEs? With regard to Eclipse, IntelliJ IDEA offers a few options.
1. Create a New IntelliJ IDEA Project as in Eclipse
To create a new project based on the settings of a particular Eclipse project, from the main menu you click File -> Open and choose the path of a .classpath or .project file. As a result, a new IntelliJ IDEA project will be generated with settings taken from Eclipse project.
2. Create a New IntelliJ IDEA Project from an Eclipse Project
To create a new project importing settings and files from an existing Eclipse project, from the main menu you click File -> Import project and proceed selecting an existing Eclipse project. In particular, you navigate to the directory and pick up the desired .project or .classpath file.
When doing so, you can choose to:
- Keep IDEA project files side by side with Eclipse or in a different folder to avoid contamination of the Eclipse folders.
- Keep IDEA and Eclipses projects in sync so that each environment detects changes from the other.
For more information, check the tutorial "Importing a Project from Eclipse".
3. Add Eclipse Projects as Modules of an Existing IntelliJ IDEA Project
To import an Eclipse module into an existing IntelliJ IDEA project, from the main menu you click File -> Import Modules and navigate to the desired .project or .classpath file.
4. Create an Eclipse Compatible Project from an IntelliJ IDEA Project
To import an Eclipse module into an existing IntelliJ IDEA project, from the main menu you click File -> Export to Eclipse. You then select the modules to export and proceed.
Finally, you can turn an existing IDEA project to use project files in the Eclipse format at any time. This will preserve the usability of the project also in Eclipse while keeping the project usable also from IntelliJ IDEA.