Static methods in interfaces in Java - Mini Project: Build & Apply

Static methods in interfaces

📖 Scenario: Imagine you are building a simple calculator app. You want to group some utility methods inside an interface to keep your code organized.

🎯 Goal: You will create an interface with a static method to add two numbers, then call this method from your main program.

📋 What You'll Learn

Create an interface called Calculator

Add a static method add in Calculator that takes two int parameters and returns their sum

Create a Main class with a main method

Call the static method add from Calculator inside main and print the result

💡 Why This Matters

🌍 Real World

Static methods in interfaces help organize utility functions related to a concept without needing to create objects.

💼 Career

Understanding static methods in interfaces is useful for writing clean, modular Java code in professional software development.

1

Create the interface

Create an interface called Calculator with no methods inside.

Java

interface Calculator {
    // Your code here
}

Need a hint?

An interface is declared with the keyword interface followed by its name.

2

Add a static method

Inside the Calculator interface, add a static method called add that takes two int parameters named a and b and returns their sum.

Java

interface Calculator {
    // Add static method add(int a, int b) here
}

Need a hint?

Static methods in interfaces have a body and use the keyword static.

3

Create the main class

Create a class called Main with a main method that takes String[] args as parameter.

Java

interface Calculator {
    static int add(int a, int b) {
        return a + b;
    }
}

class Main {
    public static void main(String[] args) {
        // Your code here
    }
}

Need a hint?

The main method is the program entry point and must be declared exactly as public static void main(String[] args).

4

Call the static method and print result

Inside the main method, call the static method add from the Calculator interface with arguments 5 and 7. Store the result in an int variable called sum. Then print sum using System.out.println.

Java

interface Calculator {
    static int add(int a, int b) {
        return a + b;
    }
}

class Main {
    public static void main(String[] args) {
        // Call Calculator.add(5, 7), store in sum, and print sum
    }
}

Need a hint?

Use Calculator.add(5, 7) to call the static method and System.out.println(sum) to print the result.