What elements or constructs are prohibited inside an interface?

In Kotlin interfaces, it is forbidden to declare:

• Fields with state (variables that store values). In interfaces, you can only declare properties without implementation or with a getter/setter without state.
• Constructors (including primary and secondary).
• Initializers (init blocks).

In interfaces, you can declare:

• Abstract methods and properties (without implementation).
• Methods with implementation (default methods).

Example:

interface MyInterface {
    val property: String  // property without state
    fun doSomething()    // abstract method
    fun defaultMethod() { // method with implementation
        println("Default implementation")
    }
}