Is it possible to declare fields inside an interface in a programming language?

In Java, within an interface, you can declare fields, but they are automatically considered:

• public
• static
• final

That is, fields in an interface are constants accessible without creating an instance.

Example:

public interface Constants {
    int MAX_SIZE = 100; // public static final by default
}

You cannot declare regular instance variables or mutable state fields in an interface.