static methods
- Java course
- Intermediate
- Lesson 50/116
- 5 min
Learn static methods inside interfaces.
Static methods inside an interface
You can define a static method inside an interface. This method is called through the interface name; it does not belong to the implementing class. It is useful for helper methods.
Example: interface Converter { static double metersToFeet(double m) { return m * 3.28084; } }. You call this method as Converter.metersToFeet(2). It is accessed through the interface name, not through an implementing class. A static method must have a body; because code that runs is needed when called. This is a clean way to group helper functions related to an interface. It is also ideal for factory methods.
Static methods as helpers
Static methods inside an interface carry helper functions related to that interface. They belong to the interface, not the implementing class; this keeps organization clean.
Example: in the Converter interface you can define a factory method like static Converter empty(). This method is independent of implementing classes. It is called as Converter.empty(). In older versions, helper methods required separate companion classes; now static methods live inside the interface. This keeps related code in one place. The call is always made through the interface name.
Practice Add a static method to the Converter interface
Define an interface Converter. Add a static double metersToFeet(double m) method; its body returns m * 3.28084;. In main call System.out.println(Converter.metersToFeet(2));.
Starter code
// Define the Converter interface
// Add a static metersToFeet method
// Print the method result in mainSample solution
interface Converter {
static double metersToFeet(double m) {
return m * 3.28084;
}
}
class Main {
public static void main(String[] args) {
System.out.println(Converter.metersToFeet(2));
}
}Expected output
6.56168
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Complete the static method call
double feet = ____.metersToFeet(2);double feet = Converter.metersToFeet(2);Explanation: A static method is called through the interface name.
2 How is a static method inside an interface called?
- Through an instance
- With new
- With super
- Through the interface name Correct answer
Explanation: It is called through the interface name; no instance needed.
3 Match the static method concepts
| Term | Meaning |
|---|---|
static |
Helper method keyword |
Converter |
Call name |
metersToFeet |
Method name |
return |
Value return |