How to access Java private field in Kotlin extension function

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How to access Java private field in Kotlin extension function

If 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'

So here is fix to resolve this problem

First of all we will pick a Field from Java class then we will enable that field to make it accessible from Kotlin code.


val field ="mPrivateField")

field.isAccessible = true

Now we can read field value as Int using Field#getInt function from instance of our ABC class (declaring class).


val it: ABC = TODO()

val value = field.getInt(it)

Now our extension method in Kotlin will look like this:

private inline fun ABC.testExtFunc():Int {
    return javaClass.getDeclaredField("mPrivateField").let {
        it.isAccessible = true
        val value = it.getInt(this)
        return@let value;

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