Why can I access a private fun outside a companion object in Kotlin?

Question

In my mind, a private function can only be accessed inside a class, but in my example the following code bindPreferenceSummaryToValue(findPreference("RestoreItem")), which is outside the companion object, is accessible. Why?

Code

class UIPreference : AppCompatPreferenceActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.layout_preference)

        fragmentManager.beginTransaction().replace(R.id.content, MyPreferenceFragment()).commit()

        setControl()
        utility.setAD(adView)
    }


    class MyPreferenceFragment : PreferenceFragment() {

        private lateinit var mContext: Context

        override fun onCreate(savedInstanceState: Bundle?) {
            super.onCreate(savedInstanceState)
            addPreferencesFromResource(R.xml.mypreference)
            mContext=this.activity
            setPreference()

            bindPreferenceSummaryToValue(findPreference("RestoreItem"))
        }
     }


     companion object {
        private val sBindPreferenceSummaryToValueListener = Preference.OnPreferenceChangeListener { preference, value ->
            val stringValue = value.toString()
            if (preference is ListPreference) {
                val listPreference = preference
                val index = listPreference.findIndexOfValue(stringValue)

                preference.setSummary(
                        if (index >= 0)
                            listPreference.entries[index]
                        else
                            preference.summary)

            }
            true
        }

        private fun bindPreferenceSummaryToValue(preference: Preference) {           
            preference.onPreferenceChangeListener = sBindPreferenceSummaryToValueListener

            sBindPreferenceSummaryToValueListener.onPreferenceChange(preference,
                    PreferenceManager
                            .getDefaultSharedPreferences(preference.context)
                            .getString(preference.key, ""))
        }
    }


}

To David Rawson

Thanks! But from https://kotlinlang.org/docs/reference/visibility-modifiers.html, it seems that "private means visible inside this class only (including all its members);" for Classes and Interfaces.

Would you please see the image?

To yole:

Thanks! I can't access a private member in the class MyB outside companion object by the following code.

class UIPreference {

    companion object {
        private val aa=1

    }

    class MyA {
        private val bar: Int =UIPreference.aa  //OK
    }

}


class MyB {
   private val bar: Int = UIPreference.aa //Failed
}

yole yole · Accepted Answer · 2018-06-04T06:32:46

In Kotlin, companion objects work effectively as a replacement for Java's static members, and visibility rules for them work in the same way. Just like in Java you can call a private static method from an instance method of a class, in Kotlin you can call a private method of a companion object from a regular method of a class.

Why can I access a private fun outside a companion object in Kotlin?

2 Answers