Is it possible to define the implementation of a method inside an interface in a programming language?

Yes, in modern versions of Java (starting from Java 8), it became possible to define method implementations inside interfaces using default methods and static methods.

• Default methods allow you to specify a standard implementation that all classes implementing the interface can use or override if necessary.
• Static methods in interfaces are methods that belong to the interface itself and are called through the interface name.

Example:

public interface MyInterface {
    void abstractMethod(); // regular abstract method

    default void defaultMethod() {
        System.out.println("Default implementation");
    }

    static void staticMethod() {
        System.out.println("Interface static method");
    }
}

This allows extending interfaces without breaking existing code by adding new methods with implementations.