intellij-sdk-code-samples/plugin_extensions_and_extension_points.md

---
layout: editable
title: Plugin Extensions and Extension Points
---

Intellij IDEA provides the concept of _extensions_ and _extension points_ that allows a plugin to interact with other plugins or with the IDEA core.

## Extension Points

If you want your plugin to allow other plugins to extend its functionality, in the plugin, you must declare one or several _extension points_.
Each extension point defines a class or an interface that is allowed to access this point.

## Extensions

If you want your plugin to extend the functionality of other plugins or the IDEA core, in the plugin, you must declare one or several _extensions_.

## How to Declare Extensions and Extension Points?

You can declare extensions and extension points in the plugin configuration file plugin.xml, within the ```<extensions>``` and ```<extensionPoints>``` sections, respectively.

*To declare an extension point*

*  In the ```<extensionPoints>``` section, insert a child element ```<extensionPoint>``` that defines the extension point name and the name of a bean class or an interface that is allowed to extend the plugin functionality in the *'name'*, *'beanClass'* and *'interface'* attributes, respectively.

To clarify this procedure, consider the following sample section of the plugin.xml file:

```xml
<extensionPoints>
     <extensionPoint name="MyExtensionPoint1" beanClass="MyPlugin.MyBeanClass1">
     <extensionPoint name="MyExtensionPoint2" interface="MyPlugin.MyInterface">
</extensionPoints>
```

The *interface* attribute sets an interface the plugin that contributes to the extension point must implement.

The *beanClass* attribute sets a bean class that specifies one or several properties annotated with the
[@Attribute](https://github.com/JetBrains/intellij-community/blob/master/xml/dom-openapi/src/com/intellij/util/xml/Attribute.java)
annotation.
The plugin that contributes to the extension point will read those properties from the plugin.xml file.
To clarify this, consider the following sample ```MyBeanClass1``` bean class used in the above plugin.xml file:

```java
public class MyBeanClass1 extends AbstractExtensionPointBean {
  @Attribute("key")
  public String key;

  @Attribute("implementationClass")
  public String implementationClass;

  public String getKey() {
    return key;
  }

  public String getClass() {
    return implementationClass;
  {

}
```
Note that to declare an extension designed to access the MyExtensionPoint1 extension point, your plugin.xml file must contain the <MyExtensionPoint1> tag with the "key" and "implementationClass" attributes set to appropriate values (see the sample plugin.xml file below).

*To declare an extension*

1. For the \<extensions\> element, set the *xmlns* (deprecated) or *defaultExtensionNs* attribute to one of the following values:

    *  _com.intellij_, if your plugin extends the IDEA core functionality.

    *  _ID of a plugin_, if your plugin extends a functionality of another plugin.

2. Add a new child element to the \<extensions\> element.
The child element name must match the name of the extension point you want the extension to access.

3. Depending on the type of the extension point, do one of the following:

    *  If the extension point was declared using the *interface* attribute, for newly added child element, set the *implementation* attribute to the name of the class that implements the specified interface.

    *  If the extension point was declared using the *beanClass* attribute, for newly added child element, set all attributes annotated with the
    [@Attribute](https://github.com/JetBrains/intellij-community/blob/master/xml/dom-openapi/src/com/intellij/util/xml/Attribute.java)
    annotations in the specified bean class.

To clarify this procedure, consider the following sample section of the plugin.xml file that defines two extensions designed to access the _appStarter_ and _applicationConfigurable_ extension points in the IDEA core and one extension to access the _MyExtensionPoint1_ extension point in a test plugin:

```xml
<!-- Declare extensions to access extension points in the IDEA core. These extension points
      have been declared using the "interface" attribute.
 -->
  <extensions defaultExtensionNs="com.intellij">
     <appStarter implementation="MyTestPackage.MyTestExtension1"></appStarter>
     <applicationConfigurable implementation="MyTestPackage.MyTestExtension2"></applicationConfigurable>
  </extensions>
 <!-- Declare extensions to access extension points in a custom plugin
      The MyExtensionPoint1 extension point has been declared using *beanClass* attribute.
 -->
  <extensions defaultExtensionNs="MyPluginID">
     <MyExtensionPoint1 key="keyValue" implementationClass="MyTestPackage.MyClassImpl"></MyExtensionPoint1>
  </extensions>
```

## How to Get the Extension Points List?

To get a list of extension points available in the *IntelliJ IDEA* core, consult the _\<extensionPoints\>_ section of the following XML configuration files:

* [LangExtensionPoints.xml](https://github.com/JetBrains/intellij-community/blob/master/platform/platform-resources/src/META-INF/LangExtensionPoints.xml)

* [PlatformExtensionPoints.xml](https://github.com/JetBrains/intellij-community/blob/master/platform/platform-resources/src/META-INF/PlatformExtensionPoints.xml)

* [VcsExtensionPoints.xml](https://github.com/JetBrains/intellij-community/blob/master/platform/platform-resources/src/META-INF/VcsExtensionPoints.xml)

## Additional Information and Samples

For samples plugins and detailed instructions on how to create your plugin that contributes to the IDEA core, refer to
[Customizing the IDEA Settings Dialog](TODO)
and
[Creation of Tool Windows](TODO).