Get parameters from URL Magento 2

By ObjectManager:

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();  
$request = $objectManager->get('Magento\Framework\App\Request\Http');  
echo $param = $request->getParam('order_id');

By Factory Method

protected $request;

public function __construct(
    ...
    \Magento\Framework\App\Request\Http $request,
    ...
) {
   $this->request = $request;
}

$this->request->getParam('order_id');

Note: Do not use objectManager directly in files as Magento 2 coding standards.

First, you need to inject \Magento\Framework\App\Request\Http at _constructfunction then using

protected $request;
    public function __construct(
        \Magento\Framework\App\Request\Http $request,
        ....//rest of parameters here
    ) {
       $this->request = $request;
       ...//rest of constructor here
    }
    public function getIddata()
    {
    // use 
    $this->request->getParams(); // all params
        return $this->request->getParam('order_id');
    }

At BLock class, you don't need to inject this class. Use

$this->getRequest() instead of $this->request.

=> Factory Method :

<?php
namespace Namespace\Module\Something;
class ClassName 
{
    protected $request;
    public function __construct(
        \Magento\Framework\App\Request\Http $request,
        ....//rest of parameters here
    ) {
       $this->request = $request;
       ...//rest of constructor here
    }
    public function getPost()
    {
        return $this->request->getParam("order_id");
    }
}

=> Object Manager :

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();  
$request = $objectManager->get('Magento\Framework\App\Request\Http');  
echo $request->getParam('order_id');

=> Note : Do not use direct object manager as magento coding format