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StackOverflowError using Singleton in Kotlin

Tags:

android

kotlin

jetbrains-ide

kotlin-android-extensions

Can anyone tell, why I'm getting a java.lang.StackOverflowError using this Kotlin class? Line 41 is if (instance == null) {

class TokenHelper protected constructor() {
    var token: String? = null
    var appId: String? = null
    var installationId: String? = null
    var userId: String? = null

    companion object {
        var instance: TokenHelper? = null
            get() {
                if (instance == null) {
                    instance = TokenHelper()
                }
                return instance
            }
    }
}

Stacktrace:

04-11 19:07:42.188 16142-16142/com.foo.bar.debug E/AndroidRuntime: FATAL EXCEPTION: main
  Process: com.foo.bar.debug, PID: 16142
  java.lang.StackOverflowError: stack size 8MB
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:0)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
      at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
    at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41
04-11 19:07:42.271 16142-16142/com.foo.bar.debug D/Error: ERR: exClass=java.lang.StackOverflowError
04-11 19:07:42.271 16142-16142/com.foo.bar.debug D/Error: ERR: exMsg=stack size 8MB
04-11 19:07:42.271 16142-16142/com.foo.bar.debug D/Error: ERR: file=TokenHelper.kt
04-11 19:07:42.271 16142-16142/com.foo.bar.debug D/Error: ERR: class=com.foo.bar.helper.TokenHelper$Companion
04-11 19:07:42.271 16142-16142/com.foo.bar.debug D/Error: ERR: method=getInstance line=0
04-11 19:07:42.282 16142-16142/com.foo.bar.debug D/Error: ERR: stack=java.lang.StackOverflowError: stack size 8MB
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:0)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
  at com.foo.bar.helper.TokenHelper$Companion.getInstance(TokenHelper.kt:41)
    at com.foo.bar.helper.TokenHelper$Companion.getInstance(
04-11 19:07:42.283 16142-16142/com.foo.bar.debug D/Error: ERR: TOTAL BYTES WRITTEN: 880768
04-11 19:07:45.527 16142-16142/com.foo.bar.debug D/Process: killProcess, pid=16142
04-11 19:07:45.528 16142-16142/com.foo.bar.debug D/Process: com.android.internal.os.RuntimeInit$UncaughtHandler.uncaughtException:113 java.lang.ThreadGroup.uncaughtException:693 java.lang.ThreadGroup.uncaughtException:690

Android Studio 2.0, Kotlin 1.0.1-2

like image 601
user3105453 Avatar asked Apr 11 '16 17:04

user3105453

2 Answers

You're calling instance getter method recursively. Change you getter definition to use field instead:

var instance: TokenHelper? = null
    get() {
        if (field == null) {
            field = TokenHelper()
        }
        return field
    }

The relevant excerpt from the documentation:

Classes in Kotlin cannot have fields. However, sometimes it is necessary to have a backing field when using custom accessors. For these purposes, Kotlin provides an automatic backing field which can be accessed using the field identifier:

var counter = 0 // the initializer value is written directly to the backing field
  set(value) {
    if (value >= 0)
      field = value
  }

The field identifier can only be used in the accessors of the property.

like image 200
miensol Avatar answered Oct 13 '22 10:10

miensol

Adapted from a comment on the original answer:

In Kotlin, you don't need all the boilerplate to declare a singleton. When declaring your class, simply make it an object like so:

object TokenHelper {
    var token: String? = null
    var appId: String? = null
    var installationId: String? = null
    var userId: String? = null
}

Then access it as follows: TokenHelper.token or from Java TokenHelper.INSTANCE.getToken().

like image 38
Kirill Rakhman Avatar answered Oct 13 '22 08:10

Kirill Rakhman
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