Why are interface variables static and final by default?

In Java, interface variables are static and final by default because that is how they are defined in the Java Language Specification (JLS).

The static modifier indicates that the variable is a class variable and belongs to the class, rather than to an instance of the class. This means that there is only one copy of the variable that is shared by all instances of the class.

The final modifier indicates that the variable is a constant and its value cannot be modified after it is initialized.

The JLS states that "All variables in an interface are implicitly public, static, and final. It is permitted to redundantly specify any or all of these modifiers for such a variable."

The reason for this design decision is that interfaces are meant to define a set of behaviors that a class can implement, rather than state. By making interface variables static and final, it ensures that they cannot be modified and that their values are the same for all implementations of the interface.

I hope this helps. Let me know if you have any questions.