With the Extract Interface refactoring you have the following options:
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.
Create an interface based on the methods of a class.
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.
Before
After
// File AClass.java
class AClass {
public static final double CONSTANT = 3.14;
public void publicMethod() {
}
public void secretMethod() {
}
}
// File AClass.java
class AClass implements AnInterface {
public void publicMethod() {
}
public void secretMethod() {
}
// File AnInterface.java
public interface AnInterface {
double CONSTANT = 3.14;
void publicMethod();
}
}
Another example of the Extract Interface refactoring, when the Rename original class and use interface where possible option is selected.
Before
After
public class FormerAClass implements AClass {
public void publicMethod() {
}
public void secretMethod() {
}
}
public interface AClass {
double CONSTANT=3.14;
void publicMethod();
}
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
}
}
Extracted Interface:
public interface AnotherInterface extends AnInterface {
}
Source class implements both interfaces.
Source class:
class AClass implements AnInterface, AnotherInterface {
public void publicMethod() {
//some code here
}
public void secretMethod() {
//some code here
}
}
Extracted Interface:
public interface AnotherInterface {
}
