In Yii2, the Component class has replaced the CComponent class from Yii1. In Yii1, components act as service locators that host a specific set of application components that provide different services for the processing of requests. Each component in Yii2 can be accessed using the following syntax:

Yii::$app->componentID

For example, the database component can be accessed using this:

Yii::$app->db

The cache component can be accessed using this:

Yii::$app->cache

Yii2 automatically registers each component at runtime via the application configuration that we mentioned in the previous section by name.

To improve performance in Yii2 applications, components are lazy-loaded or only instantiated the first time they are accessed. This means that if the cache component is never used in your application code, the cache component will never be loaded. At times, however, this can be nonideal, so to force load a component, you can bootstrap it by adding it to the bootstrap configuration option in either config/web.php or config/console.php. For instance, if we want to bootstrap the log component, we can do that as follows:

<?php return [
    'bootstrap' => [
        'log'
    ],
    […]
]

The bootstrap option behaves in a manner similar to the preload option in Yii1—any component that you want or need to be instantiated on bootstrap will be loaded if it is in the bootstrap section of your configuration file.

In Yii2, almost every class that doesn't extend from the Component class extends from the Object class. The Object class is the base class that implements the property feature. In Yii2, the property feature allows you to access a lot of information about an object, such as the __get and __set magic methods, as well as other utility functions, such as hasProperty(), canGetProperty(), and canSetProperty(). Combined, this makes objects in Yii2 extremely powerful.