To be able to show the message you need to have some reference to the context. Toast is static class you can call Toast from any activity, broadcast receiver or any class that have context
In general there are two type of classes. Ones that extend ContextWrapper class (Activity, Service, Application) and those that do not extend it (like View).
If class extends ContextWrapper then you can use this as Context. Such classes normally do not have getContext() method.
Those classes that do not extend ContextWrapper but still save and use Context normally expose getContext() function. And you cannot use this as Context in such cases.
And these two cases are mutually exclusive. At least I don't recall classes that extend ContextWrapper and have getContext at the same time.
this for more details What's the difference between the various methods to get a Context?