Hi,
My prolem is very simple, but i'm beggining with java.

I have 10 key-values: "CUSTOMER_ID" , the others are not important
What is important is that I want to have different values under the same key CUSTOMER_ID

The structure should be like this:

CUSTOMER_ID 5
CUSTOMER_ID 1
CUSTOMER_ID 4
OFFICE_ID 33
SOME_KEY 10
SOME_OTHER_KEY 123

Which structure can I use?
can I use Java Map?
List?
Other?

and how to insert this values and how to load it?
Please show me simple code