Is it possible to declare variables with a private modifier inside an interface?

In Java, it is not possible to declare variables with the private modifier inside an interface. All variables in an interface are by default:

• public
• static
• final

That is, they are effectively constants accessible to anyone using the interface.

Example:

public interface MyInterface {
    int CONSTANT = 10; // public static final by default
}

Attempting to declare a variable with the private modifier inside an interface will result in a compile-time error.

Starting from Java 9, it is possible to declare private methods inside interfaces, but not private variables.