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

• A. Yes, but only for member variables.
• B. No, only public variables are allowed in interfaces.
• C. Yes, it’s allowed for static variables only.
• D. Private and protected are allowed only in abstract interfaces.

Answer: (B)

In Java, all variables declared in an interface are implicitly public, static, and final. This means that they cannot be private or protected. The design of interfaces is meant to specify a contract that implementing classes must adhere to, and having public accessibility for variables ensures that they are accessible to implementing classes.

This rule reinforces the idea that interfaces focus on defining behavior rather than providing a mechanism for encapsulating state. While you cannot define private or protected variables within an interface, it's important to note that since all members of an interface must be public, only public variables are permitted.

Additionally, with the introduction of Java 9, private methods can be defined in interfaces for use by default methods, but this does not apply to variables. Therefore, the only acceptable access modifier for interface variables is public.