Unveiling the Java Interface: A Comprehensive Guide to Interface Types

Introduction:

In the vast world of Java programming, interfaces play a pivotal role in achieving code modularity, flexibility, and multiple inheritances. An interface defines a contract for a class, outlining the methods it must implement without specifying the implementation details. In this article, we’ll explore the different types of interfaces in Java and delve into examples to illustrate their use cases.

Regular Interfaces:
The most common type of interface, a regular interface, declares abstract methods that classes implementing the interface must provide concrete implementations for. Let’s consider a simple example:

interface Shape {
    double calculateArea();
}

class Circle implements Shape {
    private double radius;

    public Circle(double radius) {
        this.radius = radius;
    }

    @Override
    public double calculateArea() {
        return Math.PI * radius * radius;
    }
}

Here, the Shape interface defines a method calculateArea(), and the Circle class implements this interface, providing its own calculation logic.

Functional Interfaces:
Introduced in Java 8, functional interfaces have a single abstract method, making them suitable for lambda expressions and functional programming. The @FunctionalInterface annotation ensures that the interface adheres to this rule. Consider the following example: