Question

Map<String, Data> map = new HashMap<String,Data>();
map.put("jan", new Data("RED","M4A1",5,0,0));

How can I change the value RED of the Data object?, without getting all the information out of the map with the key and putting it back in, like this:

map.put("jan" new Data("Blue",
      map.get("jan").Brand,
      map.get("jan").Storage,
      map.get("jan").Sold,
      map.get("jan").Bought)); 

So how can i change 1 value of the Data Object instead of redo them all?

Answer 1

It depends on whether Data is mutable. For example, you may be able to write:

Data data = map.get("jan");
data.setColor("Blue");

Don’t forget that the map only contains a reference to the object, so if you change the data within the object, that change will be seen if someone fetches the reference from the map later.

Or if it’s immutable, it could potentially have a withColor method, so you could write:

Data data = map.get("jan");
map.put("jan", data.withColor("Blue"));

Without knowing more about your Data type (which I hope isn’t the real name of your class) it’s hard to say any more.

(I also hope your class doesn’t really have Pascal-cased fields, and I hope those fields are private, but that’s a different matter…)