Déjà vu and dreaming are closely related to memory and memory formation. However, they have nothing to do with future events. The brain cannot recall what it never has processed in the past.
Déjà vu is thought to be related to the tip-of-the-tongue feeling, in the sense that it is a memory phenomenon. It can occur when someone encounters a scenario that’s similar to an actual memory, but they fail to recall the memory. In other words, it's not an actual memory but an erroneous retrieval of a memory, if you like (sources: PsychCentral & New Scientist).
Dreams are basically stories and images our mind creates while we sleep. It has been proposed that dreams reflect biological processes of long-term memory consolidation. Consolidation strengthens the neural representations of recent events (i.e., their memories) and embeds these new memory fragments into older, existing memories. This also maintains the stability of existing memory representations in the face of subsequent experiences (Payne & Nadel, 2004). In sleeping rodents, for example, neurons in the hippocampus fire in patterns remarkably similar to those recorded during a previous maze-running session—almost as if the animals replay the experience in their sleep (source: Science Magazine).
In all, déjà vu and dreaming are indeed closely related to memory, and memory formation. However, they have nothing to do with future events. The brain cannot recall what never has perceived in the past. Hence, déjà vu experiences and dreams have nothing to do with what the future may bring, other than cases of pure coincidence.
- Payne & Nadel, Learn Mem (2004); 11(6): 671–8