What is the role of interfaces in the Java programming language and what are they used for?

In Java, interfaces define a contract that a class must implement, which is a set of methods without implementations. They allow:

• Providing abstraction and separating the definition of behavior from its implementation.
• Implementing multiple inheritance of types, as a class can implement multiple interfaces.
• Increasing flexibility and extensibility of the code, allowing working with objects through interfaces rather than concrete classes.

Example of an interface and its implementation:

interface Drawable {
    void draw();
}

class Circle implements Drawable {
    public void draw() {
        System.out.println("Drawing a circle");
    }
}

Interfaces are widely used for designing modular and testable systems.