Access Modifiers

control how much of an object is visible to the rest of Java program, and packages provide the highest level of control over object visibility.

private - accessible to the classes only.
protected - accessible to class, package, and subclasses
[default] - accessible to the class and package
public - accessible to global

Can we define private and protected modifiers for variables in interfaces?

Having private or protected members in an interface doesn't make sense conceptually.