---
title: "Calls and callbacks"
url: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/java-native-interface-integration/calls-and-callbacks-jni"
source_url: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/java-native-interface-integration/calls-and-callbacks-jni.md"
canonical: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/java-native-interface-integration/calls-and-callbacks-jni"
last_modified: "2019-04-26T13:09:00+02:00"
language: "en"
---

# Calls and callbacks

[View source](/point-of-sale/classic-library-deprecation/classic-library-integrations/java-native-interface-integration/calls-and-callbacks-jni.md)

Calls and callbacks follow this flow:

1. Invoke a method to perform a specific action.

2. The invoked method invokes the synchronization helper method, specifying a parameter to determine which callback should be returned.

3. The synchronization helper method waits until one of the following occurs:

   1. The system returns a callback
   2. A time-out of 20 seconds
   3. An exception.

    

4. if the system returns a callback, the main flow resumes, and the application handles and processes the information returned in the callback.

## Callback Parameter Order

The order of parameters is defined in the C library defines the order of parameters but can not enforce it. 

The `createTender` callback returns a tender object. Use this to execute subsequent actions on a tender. Evaluate other arguments using the provided helper methods.

Error Messages can be used directly in logging or feedback without helper methods.

## Actionable vs. Informational Callbacks

Several callbacks occur during the processing of a tender. There are two types of callback: Actionable and Informational.

* Actionable callbacks require action to complete the transaction.
* Informational callbacks can be logged but are not required to complete a transaction.

Actionable callbacks:

* [Signature Callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/java-native-interface-integration/key-steps-jni/process-a-basic-transaction-jni/handle-the-signature-callback-jni)
* [AdditionalData Callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/java-native-interface-integration/key-steps-jni/process-a-basic-transaction-jni/handle-the-additional-data-callback-jni)
* [PrintReceipt Callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/java-native-interface-integration/key-steps-jni/process-a-basic-transaction-jni/handle-the-print-receipt-callback-jni)

Informational callbacks:

* [Progress Event Callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/java-native-interface-integration/key-steps-jni/process-a-basic-transaction-jni/handle-progress-events-jni)
* [DCC Callback](/point-of-sale/classic-library-deprecation/classic-library-integrations/java-native-interface-integration/extras-jni/handle-dynamic-currency-conversion-jni)