What's Kotlin Backing Field For?

Question

As a Java developer, the concept of a backing field is a bit foreign to me. Given:

class Sample {
    var counter = 0 // the initializer value is written directly         


        

Answer 1

Backing fields are good for running validation or triggering events on state change. Think of the times you've added code to a Java setter/getter. Backing fields would be useful in similar scenarios. You would use backing fields when you needed to control or have visibility over setters/getters.

When assigning the field with the field name itself, you're actually invoking the setter (i.e. set(value)). In the example you have, this.counter = value would recurse into set(value) until we overflow our stack. Using field bypasses the setter (or getter) code.