For HashMap like i.e. Key,Value pair -> MongoDB
would be a good choice since you store documents in it in BSON (Binary JSON) structure.
For Tree/Graph like structures -> Neo4j
would be a good choice I guess.
質問
What external database can I use to work with my java application except Microsoft Access? I need a tree like structure or a hashmap and not relational tables.
他のヒント
Well, relational tables can be used to do what a tree or a hashmap does, very easily. So something like MySQL or PostgreSQL could easily meet your needs.
If you really want a treelike/hashmap-like database, look at MapDB. It's very fast, and provides both trees and hashmaps.