diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java
index 909da78def7..26903cc47d1 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java
@@ -986,10 +986,10 @@ public abstract class AbstractJavaCodegen extends DefaultCodegen implements Code
                         final_values.add(element.asText());
                     });
                 } else if (schema.getDefault() instanceof Collection) {
-                    var _default = (Collection<String>) schema.getDefault();
+                    var _default = (Collection<Object>) schema.getDefault();
                     List<String> final_values = _values;
                     _default.forEach((element) -> {
-                        final_values.add(element);
+                        final_values.add(String.valueOf(element));
                     });
                 } else { // single value
                     _values = java.util.Collections.singletonList(String.valueOf(schema.getDefault()));
diff --git a/modules/openapi-generator/src/test/resources/3_0/java/petstore-with-fake-endpoints-models-for-testing-okhttp-gson.yaml b/modules/openapi-generator/src/test/resources/3_0/java/petstore-with-fake-endpoints-models-for-testing-okhttp-gson.yaml
index 92dafde5e0d..af48b1a1136 100644
--- a/modules/openapi-generator/src/test/resources/3_0/java/petstore-with-fake-endpoints-models-for-testing-okhttp-gson.yaml
+++ b/modules/openapi-generator/src/test/resources/3_0/java/petstore-with-fake-endpoints-models-for-testing-okhttp-gson.yaml
@@ -1155,6 +1155,26 @@ paths:
       responses:
         200:
           description: OK
+  /fake/parameter-array-number:
+    get:
+      tags:
+        - another_fake
+      summary: parameter array number default value
+      operationId: getParameterArrayNumber
+      parameters:
+        - name: array
+          in: header
+          description: array integer
+          required: true
+          schema:
+            type: array
+            items:
+              type: integer
+            default:
+              - 1
+      responses:
+        200:
+          description: OK
   /values:
     get:
       tags:
diff --git a/samples/client/petstore/java/okhttp-gson/README.md b/samples/client/petstore/java/okhttp-gson/README.md
index 87b6205eeac..8b0c31d27db 100644
--- a/samples/client/petstore/java/okhttp-gson/README.md
+++ b/samples/client/petstore/java/okhttp-gson/README.md
@@ -114,6 +114,7 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 Class | Method | HTTP request | Description
 ------------ | ------------- | ------------- | -------------
 *AnotherFakeApi* | [**call123testSpecialTags**](docs/AnotherFakeApi.md#call123testSpecialTags) | **PATCH** /another-fake/dummy | To test special tags
+*AnotherFakeApi* | [**getParameterArrayNumber**](docs/AnotherFakeApi.md#getParameterArrayNumber) | **GET** /fake/parameter-array-number | parameter array number default value
 *AnotherFakeApi* | [**getParameterStringNumber**](docs/AnotherFakeApi.md#getParameterStringNumber) | **GET** /fake/parameter-string-number | parameter string number
 *DefaultApi* | [**fooGet**](docs/DefaultApi.md#fooGet) | **GET** /foo | 
 *FakeApi* | [**fakeHealthGet**](docs/FakeApi.md#fakeHealthGet) | **GET** /fake/health | Health check endpoint
diff --git a/samples/client/petstore/java/okhttp-gson/api/openapi.yaml b/samples/client/petstore/java/okhttp-gson/api/openapi.yaml
index 338e360f674..b6e37f7b6fc 100644
--- a/samples/client/petstore/java/okhttp-gson/api/openapi.yaml
+++ b/samples/client/petstore/java/okhttp-gson/api/openapi.yaml
@@ -1188,6 +1188,29 @@ paths:
       tags:
       - another_fake
       x-accepts: application/json
+  /fake/parameter-array-number:
+    get:
+      operationId: getParameterArrayNumber
+      parameters:
+      - description: array integer
+        explode: false
+        in: header
+        name: array
+        required: true
+        schema:
+          default:
+          - 1
+          items:
+            type: integer
+          type: array
+        style: simple
+      responses:
+        "200":
+          description: OK
+      summary: parameter array number default value
+      tags:
+      - another_fake
+      x-accepts: application/json
   /values:
     get:
       description: ""
diff --git a/samples/client/petstore/java/okhttp-gson/docs/AnotherFakeApi.md b/samples/client/petstore/java/okhttp-gson/docs/AnotherFakeApi.md
index 4ab44475b39..6cca209c72b 100644
--- a/samples/client/petstore/java/okhttp-gson/docs/AnotherFakeApi.md
+++ b/samples/client/petstore/java/okhttp-gson/docs/AnotherFakeApi.md
@@ -5,6 +5,7 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 | Method | HTTP request | Description |
 |------------- | ------------- | -------------|
 | [**call123testSpecialTags**](AnotherFakeApi.md#call123testSpecialTags) | **PATCH** /another-fake/dummy | To test special tags |
+| [**getParameterArrayNumber**](AnotherFakeApi.md#getParameterArrayNumber) | **GET** /fake/parameter-array-number | parameter array number default value |
 | [**getParameterStringNumber**](AnotherFakeApi.md#getParameterStringNumber) | **GET** /fake/parameter-string-number | parameter string number |
 
 
@@ -70,6 +71,65 @@ No authorization required
 |-------------|-------------|------------------|
 | **200** | successful operation |  -  |
 
+<a id="getParameterArrayNumber"></a>
+# **getParameterArrayNumber**
+> getParameterArrayNumber(array)
+
+parameter array number default value
+
+### Example
+```java
+// Import classes:
+import org.openapitools.client.ApiClient;
+import org.openapitools.client.ApiException;
+import org.openapitools.client.Configuration;
+import org.openapitools.client.models.*;
+import org.openapitools.client.api.AnotherFakeApi;
+
+public class Example {
+  public static void main(String[] args) {
+    ApiClient defaultClient = Configuration.getDefaultApiClient();
+    defaultClient.setBasePath("http://petstore.swagger.io:80/v2");
+
+    AnotherFakeApi apiInstance = new AnotherFakeApi(defaultClient);
+    List<Integer> array = Arrays.asList(); // List<Integer> | array integer
+    try {
+      apiInstance.getParameterArrayNumber(array);
+    } catch (ApiException e) {
+      System.err.println("Exception when calling AnotherFakeApi#getParameterArrayNumber");
+      System.err.println("Status code: " + e.getCode());
+      System.err.println("Reason: " + e.getResponseBody());
+      System.err.println("Response headers: " + e.getResponseHeaders());
+      e.printStackTrace();
+    }
+  }
+}
+```
+
+### Parameters
+
+| Name | Type | Description  | Notes |
+|------------- | ------------- | ------------- | -------------|
+| **array** | [**List&lt;Integer&gt;**](Integer.md)| array integer | |
+
+### Return type
+
+null (empty response body)
+
+### Authorization
+
+No authorization required
+
+### HTTP request headers
+
+ - **Content-Type**: Not defined
+ - **Accept**: Not defined
+
+### HTTP response details
+| Status code | Description | Response headers |
+|-------------|-------------|------------------|
+| **200** | OK |  -  |
+
 <a id="getParameterStringNumber"></a>
 # **getParameterStringNumber**
 > getParameterStringNumber(stringNumber)
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/AnotherFakeApi.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
index 2711ffbb8a6..f7529bc7476 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
@@ -196,6 +196,127 @@ public class AnotherFakeApi {
         localVarApiClient.executeAsync(localVarCall, localVarReturnType, _callback);
         return localVarCall;
     }
+    /**
+     * Build call for getParameterArrayNumber
+     * @param array array integer (required)
+     * @param _callback Callback for upload/download progress
+     * @return Call to execute
+     * @throws ApiException If fail to serialize the request body object
+     * @http.response.details
+     <table summary="Response Details" border="1">
+        <tr><td> Status Code </td><td> Description </td><td> Response Headers </td></tr>
+        <tr><td> 200 </td><td> OK </td><td>  -  </td></tr>
+     </table>
+     */
+    public okhttp3.Call getParameterArrayNumberCall(List<Integer> array, final ApiCallback _callback) throws ApiException {
+        String basePath = null;
+        // Operation Servers
+        String[] localBasePaths = new String[] {  };
+
+        // Determine Base Path to Use
+        if (localCustomBaseUrl != null){
+            basePath = localCustomBaseUrl;
+        } else if ( localBasePaths.length > 0 ) {
+            basePath = localBasePaths[localHostIndex];
+        } else {
+            basePath = null;
+        }
+
+        Object localVarPostBody = null;
+
+        // create path and map variables
+        String localVarPath = "/fake/parameter-array-number";
+
+        List<Pair> localVarQueryParams = new ArrayList<Pair>();
+        List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
+        Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+        Map<String, String> localVarCookieParams = new HashMap<String, String>();
+        Map<String, Object> localVarFormParams = new HashMap<String, Object>();
+
+        if (array != null) {
+            localVarHeaderParams.put("array", localVarApiClient.parameterToString(array));
+        }
+
+        final String[] localVarAccepts = {
+        };
+        final String localVarAccept = localVarApiClient.selectHeaderAccept(localVarAccepts);
+        if (localVarAccept != null) {
+            localVarHeaderParams.put("Accept", localVarAccept);
+        }
+
+        final String[] localVarContentTypes = {
+        };
+        final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
+        if (localVarContentType != null) {
+            localVarHeaderParams.put("Content-Type", localVarContentType);
+        }
+
+        String[] localVarAuthNames = new String[] {  };
+        return localVarApiClient.buildCall(basePath, localVarPath, "GET", localVarQueryParams, localVarCollectionQueryParams, localVarPostBody, localVarHeaderParams, localVarCookieParams, localVarFormParams, localVarAuthNames, _callback);
+    }
+
+    @SuppressWarnings("rawtypes")
+    private okhttp3.Call getParameterArrayNumberValidateBeforeCall(List<Integer> array, final ApiCallback _callback) throws ApiException {
+        // verify the required parameter 'array' is set
+        if (array == null) {
+            throw new ApiException("Missing the required parameter 'array' when calling getParameterArrayNumber(Async)");
+        }
+
+        return getParameterArrayNumberCall(array, _callback);
+
+    }
+
+    /**
+     * parameter array number default value
+     * 
+     * @param array array integer (required)
+     * @throws ApiException If fail to call the API, e.g. server error or cannot deserialize the response body
+     * @http.response.details
+     <table summary="Response Details" border="1">
+        <tr><td> Status Code </td><td> Description </td><td> Response Headers </td></tr>
+        <tr><td> 200 </td><td> OK </td><td>  -  </td></tr>
+     </table>
+     */
+    public void getParameterArrayNumber(List<Integer> array) throws ApiException {
+        getParameterArrayNumberWithHttpInfo(array);
+    }
+
+    /**
+     * parameter array number default value
+     * 
+     * @param array array integer (required)
+     * @return ApiResponse&lt;Void&gt;
+     * @throws ApiException If fail to call the API, e.g. server error or cannot deserialize the response body
+     * @http.response.details
+     <table summary="Response Details" border="1">
+        <tr><td> Status Code </td><td> Description </td><td> Response Headers </td></tr>
+        <tr><td> 200 </td><td> OK </td><td>  -  </td></tr>
+     </table>
+     */
+    public ApiResponse<Void> getParameterArrayNumberWithHttpInfo(List<Integer> array) throws ApiException {
+        okhttp3.Call localVarCall = getParameterArrayNumberValidateBeforeCall(array, null);
+        return localVarApiClient.execute(localVarCall);
+    }
+
+    /**
+     * parameter array number default value (asynchronously)
+     * 
+     * @param array array integer (required)
+     * @param _callback The callback to be executed when the API call finishes
+     * @return The request call
+     * @throws ApiException If fail to process the API call, e.g. serializing the request body object
+     * @http.response.details
+     <table summary="Response Details" border="1">
+        <tr><td> Status Code </td><td> Description </td><td> Response Headers </td></tr>
+        <tr><td> 200 </td><td> OK </td><td>  -  </td></tr>
+     </table>
+     */
+    public okhttp3.Call getParameterArrayNumberAsync(List<Integer> array, final ApiCallback<Void> _callback) throws ApiException {
+
+        okhttp3.Call localVarCall = getParameterArrayNumberValidateBeforeCall(array, _callback);
+        localVarApiClient.executeAsync(localVarCall, _callback);
+        return localVarCall;
+    }
     /**
      * Build call for getParameterStringNumber
      * @param stringNumber string number (required)