Explain what is meant by complete duplication of an object with its nested structures.

Deep copying an object with its nested structures means creating a new copy of the object, including all the objects it references, recursively. As a result, an independent copy is obtained, and changes to it do not affect the original.

In Android (Java/Kotlin), shallow copying an object copies only the references to nested objects, not the nested objects themselves. This can lead to unexpected side effects when modifying nested data.

Example of deep copying:

 data class Address(var city: String)
 data class Person(var name: String, var address: Address)

fun deepCopyPerson(original: Person): Person {
    val addressCopy = Address(original.address.city)
    return Person(original.name, addressCopy)
}

val person1 = Person("Ivan", Address("Moscow"))
val person2 = deepCopyPerson(person1)
person2.address.city = "Saint Petersburg"
// person1.address.city will remain "Moscow"

Thus, deep copying guarantees that all nested objects will also be copied, not just references to them.