I am using Json-Simple in Kotlin.
In what situations could this cast:
val jsonObjectIterable = jsonArray as Iterable<JSONObject>
Become dangerous? jsonArray is a JSONArray object.
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2 Answers
You can cast it successfully, since JSONArray is-A Iterable. but it can't make sure each element in JSONArray is a JSONObject.
The JSONArray is a raw type List, which means it can adding anything, for example:
val jsonArray = JSONArray()
jsonArray.add("string")
jsonArray.add(JSONArray())
When the code operates on a downcasted generic type Iterable<JSONObject> from a raw type JSONArray, it maybe be thrown a ClassCastException, for example:
val jsonObjectIterable = jsonArray as Iterable<JSONObject>
// v--- throw ClassCastException, when try to cast a `String` to a `JSONObject`
val first = jsonObjectIterable.iterator().next()
So this is why become dangerous. On the other hand, If you only want to add JSONObjecs into the JSONArray, you can cast a raw type JSONArray to a generic type MutableList<JSONObject>, for example:
@Suppress("UNCHECKED_CAST")
val jsonArray = JSONArray() as MutableList<JSONObject>
// v--- the jsonArray only can add a JSONObject now
jsonArray.add(JSONObject(mapOf("foo" to "bar")))
// v--- there is no need down-casting here, since it is a Iterable<JSONObject>
val jsonObjectIterable:Iterable<JSONObject> = jsonArray
val first = jsonObjectIterable.iterator().next()
println(first["foo"])
// ^--- return "bar"
2 Comments
pavlos163
I see. This jsonArray is the response of an API I trust (and is supposed to return a JSONArray of underlying JSONObjects). Therefore I could consider this as completely safe, right?
holi-java
@pk1914 No. the json data type is not only have
JSONObject&JSONArray , but also have string,boolean,number. and a JSONArray also can add any type of Object, e.g: add another json array add(JSONArray()).Following is rather a simple implementation.
Suppose Your Object is Person
data class Person( val ID: Int, val name: String): Serializable
val gson = Gson()
val persons: Array<Person> = gson.fromJson(responseSTRING, Array<Person>::class.java)
Now persons is an Array of Person
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