Extract interface
With the Extract Interface refactoring you have three options:
- Create an interface based on the methods of a class without applying the new interface immediately.
- Create an interface and apply it to the source code.
- Rename the original class, and it implements the newly created interface. In such case, IntelliJ IDEA changes all usages of the original class to use the interface where possible.
In addition, static final fields, declared in the initial class, can be moved to an interface. As a result, an interface will be created containing the specific methods and fields. Thereby, the specified class methods become implementations of the corresponding interface methods.
Examples
Here we have a class, and perform Extract Interface refactoring to create an interface based on the methods of the class.
Another example of the Extract Interface refactoring, when the Rename original class and use interface where possible option is selected.
You can extract an interface from the class that already implements another interface. Let's extract
interface from the class that implements AnInterface. Depending on whether we
want
AnotherInterface
(extracted interface) to extend the
AnInterface
(existing one) or we want source
AClass
to implement them both, we will get the following code:
Extracted Interface extends the existing one:
class AClass implements AnotherInterface {
public void publicMethod() {
//some code here
}
public void secretMethod() {
//some code here
}
}public interface AnotherInterface extends AnInterface {
}Source class implements both interfaces.
class AClass implements AnInterface, AnotherInterface {
public void publicMethod() {
//some code here
}
public void secretMethod() {
//some code here
}
}public interface AnotherInterface {
}Extracting an interface
- Select a class in the Project view, Structure view, or place the caret anywhere within a class in the editor.
- On the main menu or on the context menu of the selection, choose . The Extract Interface dialog box appears.
-
To extract a new interface, select the
Extract Interface
option and
specify the name for the new interface.
To rename the original class and make it an implementation of the newly created interface, select the Rename original class and use interface where possible option and specify the new name for the original class. IntelliJ IDEA will alter all original class usages to the usages of the implementing only where it is still necessary. - Specify the package, where the new interface will be located.
- Select the class members you want to be listed in the interface in the Members to form interface area. The list shows all the methods of the class, as well as final static fields (constants).
- In the JavaDoc area, select the action to be applied on the JavaDoc.
- Click Refactor to proceed.
- Click Refactor when ready. If IntelliJ IDEA shows you a Refactoring Preview in the Find tool window, review the suggested changes. To have the interface extracted and the proposed changes applied, click Do Refactor.