Answer:
Intrapersonal communication.
Step-by-step explanation:
Intrapersonal communication is a type of communication in which an individual engages in communication with one's self, for instance, self-talk, imagination, or even recollecting memories or thoughts, etc.
In the given instance, Gavin is engaged in self-talk. Gavin is saying to himself that he will take a walk that day. As explained above, self-talk is an intrapersonal communication, the given sentence exemplifies the same.
Therefore, the type of communication presented in the given statement is intrapersonal communication.