How to remove object manager

Question

Below is my code how to write this code without object manager.

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
        //get current product
        $product = $objectManager->get('Magento\Framework\Registry')->registry('current_product');
        $productId = $product->getId();

Answer 1

I assume you have this code in a class.
If you do, you can do this.

change the class constructor and add Magento\Framework\Registry as a parameter.
Like this:

protected $registry;
public function __construct(
    ....
    \Magento\Framework\Registry $registry,
    ...
) {
    ...
    $this->registry = $registry;
    ....
}

and now you can make your code look like

$product = $this->registry->registry('current_product');
$productId = ($product) ? $product->getId() : null;