---
title: Project
---

In IntelliJ IDEA, a project encapsulates all your source code, libraries, build instructions into a single organizational unit.
Everything you do in IntelliJ IDEA, is done within the context of a project.
A project defines some collections referred to as modules and libraries.
Depending on the logical and functional requirements to the project, you can create a single-module or a multi-module project.

## Working with Projects

*IntelliJ Platform* stores the project configuration data in XML files.
The list of those files depends on the plugin
[project](http://www.jetbrains.com/idea/webhelp/project.html)
format.
For file-based format projects, the information core to the project itself (e.g. location of the component modules, compiler settings, etc.) is stored in the <%project name%>.IPR file.
The information about modules the project includes is stored in <%module name%>.IML files.
Module files are created for each module.

For directory-based format projects, the project and workspace settings are stored in a number of XML files under the <%Project home directory%>/.idea directory.
Each XML file is responsible for its own set of settings and can be recognized by its name: projectCodeStyle.xml, encodings.xml, vcs.xml etc.
As for the file-based format projects, .IML files describe modules.

Main classes providing work with the project model are located in the package
[projectModel-api.openapi](https://github.com/JetBrains/intellij-community/tree/master/platform/projectModel-api/src/com/intellij/openapi).
Basic API classes and interfaces for the concepts of
[project](https://github.com/JetBrains/intellij-community/blob/master/platform/core-api/src/com/intellij/openapi/project/Project.java),
[module](https://github.com/JetBrains/intellij-community/blob/master/platform/core-api/src/com/intellij/openapi/module/Module.java),
[application](https://github.com/JetBrains/intellij-community/blob/master/platform/core-api/src/com/intellij/openapi/application/Application.java),
and
[component](https://github.com/JetBrains/intellij-community/blob/master/platform/core-api/src/com/intellij/openapi/components/ProjectComponent.java)
are placed in the
[core-api.openapi](https://github.com/JetBrains/intellij-community/tree/master/platform/core-api/src/com/intellij/openapi)
package.


### Finding Source Roots

To get an array of all the source roots for a project use 
```ProjectRootManager.getContentSourceRoots()``` 
method like this code snippet shows:


```java
VirtualFile[] vFiles = ProjectRootManager.getInstance(project).getContentSourceRoots();
```


### Checking if File Belongs to a Project

Use 
[ProjectFileIndex.java](https://github.com/JetBrains/intellij-community/blob/master/platform/projectModel-api/src/com/intellij/openapi/roots/ProjectFileIndex.java)
to get this information.

### Getting an Instance of the ProjectFileIndex Interface

Use the ProjectRootManager.getFileIndex() method. For example:

```java
ProjectFileIndex projectFileIndex = ProjectRootManager.getInstance(project).getFileIndex();
```

Note that this method returns `null` if the file does not belong to any module.
You can also use the ProjectFileIndex.getContentRootForFile() method to get the module content root to which the specified file or directory belongs:

```java
VirtualFile moduleContentRoot = ProjectRootManager.getInstance(project).getFileIndex().getContentRootForFile(virtualFileOrDirectory);
``` 

## Changing the project structure

Utility classes which can be used for modifying a project structure can be found in the package
[projectModel-impl.openapi](https://github.com/JetBrains/intellij-community/blob/master/platform/projectModel-impl/src/com/intellij/openapi).
It's
[roots](https://github.com/JetBrains/intellij-community/blob/master/platform/projectModel-impl/src/com/intellij/openapi/roots/)
subpackage contains instances and utilities meant to work with project and module source roots, including
[ModuleRootModificationUtil.java](https://github.com/JetBrains/intellij-community/blob/master/platform/projectModel-api/src/com/intellij/openapi/roots/ModuleRootModificationUtil.java)
and
[ProjectRootUtil.java](https://github.com/JetBrains/intellij-community/blob/master/platform/projectModel-impl/src/com/intellij/openapi/projectRoots/impl/ProjectRootUtil.java)

Refer to the
[basic example](https://github.com/JetBrains/intellij-sdk/blob/master/code_samples/project_model/src/com/intellij/tutorials/project/model/ModificationAction.java)
of on-the-fly project structure modification to learn how it can be implemented.