What is dependency injection in Magento 2?

Dependency Injection

Dependency Injection means to remove the direct dependency of the objects with class
and use a third class to create objects for that class which is ObjectManager in Magento2.
================================================================================
class CustomInfo
{
private $custom;
public function __construct($customdataone, $customdatatwo)
{
$this->customer = new Custom($customdataone, $customdatatwo);
}

public function getCustomdata()
{
return $this->custom;
}
}
===============================================================================

class CustomInfo
{
private $custom;
public function __construct(custom $custom)
{
$this->custom = $custom;
}

public function getCustom()
{
return $this->custom;
}
================================================================================
A dependency is an object that can be used
and an injection is the passing of a dependency to a dependent object that would use it

There are three types of Dependency Injection: Constructor Injection, Setter Injection and Interface Injection.
Magento 2 uses Constructor Injection

Dependency Injection is an alternative to Mage class used in Magento 1.
Magento 2 uses Automatic Dependency Injection.
Magento 2 uses Constructor Dependency Injection.
Using Constructor for DI is a must.
Instance Configurations can be specified at three levels:

app/etc/di/*.xml
{moduleDir}/etc/di.xml
{moduleDir}/etc/{areaCode}/di.xml

Dependency Injection is a great way to reduce tight coupling between application codebase.
Rather than hard-coding dependencies, you can inject the list of object that a class may need.
Dependency Injection also enables you to manage future changes and other complexity in your codes.

Manifest Desires-Click Here