Kotlin extension function access Java private field

user_706387 0
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I'd like to access Java's private field when using Kotlin extension function.

Suppose I have a Java class ABC. ABC has only one private field mPrivateField. I'd like to write an extension function in Kotlin which uses that field for whatever reason. 

public class ABC {
    private int mPrivateField;

}

the Kotlin function would be:

private fun ABC.testExtFunc() {
    val canIAccess = this.mPrivateField;
}

the error I'm getting is:

Cannot access 'mPrivateField': It is private in 'ABC'

Any way of getting around that limitation?

kotlin-interop kotlin-extension kotlin
5 Answers

Get private variable using below extension functions

fun <T : Any> T.getPrivateProperty(variableName: String): Any? {
    return javaClass.getDeclaredField(variableName).let { field ->
        field.isAccessible = true
        return@let field.get(this)
    }
}

Set private variable value get the variable

fun <T : Any> T.setAndReturnPrivateProperty(variableName: String, data: Any): Any? {
    return javaClass.getDeclaredField(variableName).let { field ->
        field.isAccessible = true
        field.set(this, data)
        return@let field.get(this)
    }
}

Get variable use:

val bool = <your_class_object>.getPrivateProperty("your_variable") as String

Set and get variable use:

val bool = <your_class_object>.setAndReturnPrivateProperty("your_variable", true) as Boolean
val str = <your_class_object>.setAndReturnPrivateProperty("your_variable", "Hello") as String
user_15488240

Extending holi-java's answer with a generic type:

  1. Create extension
fun<T: Any> T.accessField(fieldName: String): Any? {
    return javaClass.getDeclaredField(fieldName).let { field ->
        field.isAccessible = true
        return@let field.get(this)
    }
}
  1. Access private field
val field = <your_object_instance_with_private_field>
                .accessField("<field_name>")
                    as <object_type_of_field_name>

Example:

class MyClass {

    private lateinit var mObject: MyObject

}

val privateField = MyClass()
                .accessField("mObject")
                    as MyObject
user_15730360
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