Filters

Filters are one most used concepts in WordPress like actions.

You can add filters in init & onAdmin methods.

addFilter method

addFilter method is defined as so:

public function addFilter(string $hook, array $callback, int $priority = 10, int $accepted_args = 1)
    {
        $this->validateCallback($callback);
        $this->filters[] = $this->getHook($hook, $callback, $priority, $accepted_args);
    }

You should use this method like so:

$this->addFilter();

addFilter parameters

There is no difference between addFilter and addAction parameters so read Actions