Magento2 rewrite: product resource collection class does not effect on functions

I have rewrite catalog product resource collection MagentoCatalogModelResourceModelProductCollection.

Class override successfully but functions override is not working.

Suppose, i want overrider setOrder()function. But it does not works . Always calling Core function instead of rewrite class function

Class

<?php
namespace AmitBeraCoreRewriteModelRewriteCatalogResourceModelProduct;

class Collection extends MagentoCatalogModelResourceModelProductCollection
{

    protected $appState;
    public function __construct(
        MagentoFrameworkDataCollectionEntityFactory $entityFactory,
        PsrLogLoggerInterface $logger,
        MagentoFrameworkDataCollectionDbFetchStrategyInterface $fetchStrategy,
        MagentoFrameworkEventManagerInterface $eventManager,
        MagentoEavModelConfig $eavConfig,
        MagentoFrameworkAppResourceConnection $resource,
        MagentoEavModelEntityFactory $eavEntityFactory,
        MagentoCatalogModelResourceModelHelper $resourceHelper,
        MagentoFrameworkValidatorUniversalFactory $universalFactory,
        MagentoStoreModelStoreManagerInterface $storeManager,
        MagentoFrameworkModuleManager $moduleManager,
        MagentoCatalogModelIndexerProductFlatState $catalogProductFlatState,
        MagentoFrameworkAppConfigScopeConfigInterface $scopeConfig,
        MagentoCatalogModelProductOptionFactory $productOptionFactory,
        MagentoCatalogModelResourceModelUrl $catalogUrl,
        MagentoFrameworkStdlibDateTimeTimezoneInterface $localeDate,
        MagentoCustomerModelSession $customerSession,
        MagentoFrameworkStdlibDateTime $dateTime,
        MagentoFrameworkAppState $appState,
        MagentoCustomerApiGroupManagementInterface $groupManagement,
        MagentoFrameworkDBAdapterAdapterInterface $connection = null
    ) {
        parent::__construct(
                $entityFactory,
                $logger,
                $fetchStrategy,
                $eventManager,
                $eavConfig,
                $resource,
                $eavEntityFactory,
                $resourceHelper,
                $universalFactory,
                $storeManager,
                $moduleManager,
                $catalogProductFlatState,
                $scopeConfig,
                $productOptionFactory,
                $catalogUrl,
                $localeDate,
                $customerSession,
                $dateTime,
                $groupManagement,
                        $connection
            );
        $this->_appState = $appState;

    }
   public function setOrder($attribute, $dir = MagentoFrameworkDBSelect::SQL_DESC)
    {
        echo __METHOD__;
        exit;
        if ($attribute == 'price') {
            $this->addAttributeToSort($attribute, $dir);
        } else {
            parent::setOrder($attribute, $dir);
        }
        return $this;
    }


}

module.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNameSpaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="AmitBera_CoreRewrite" setup_version="2.0.0">
        <sequence>
            <module name="Magento_Catalog"/> 
            <module name="Magento_CatalogSearch"/>         
            <module name="Magento_Checkout"/>
            <module name="Magento_Sales"/>
            <module name="Magento_Quote"/>
            <module name="Magento_Vault"/>
            <module name="Magento_OfflineShipping"/>           
        </sequence>     
    </module>
</config>

di.xml

<?xml version="1.0" encoding="UTF-8"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
       <preference for="MagentoCatalogModelResourceModelProductCollection" 
        type="AmitBeraCoreRewriteModelRewriteCatalogResourceModelProductCollection" />
</config>   

Whenever use

$objectManager = MagentoFrameworkAppObjectManager::getInstance();
/** @var MagentoCatalogModelResourceModelProductCollection $productCollection */
$productCollection = $objectManager->create('MagentoCatalogModelResourceModelProductCollection');
echo get_class($productCollection );

result:

AmitBeraCoreRewriteModelRewriteCatalogResourceModelProductCollectionInterceptor

Question:

• i donot understand why i am not able to override function
  setorder()
• Why echo get_class($productCollection ); give Interceptor class

AmitBeraCoreRewriteModelRewriteCatalogResourceModelProductCollectionInterceptor