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private instance variable of Map type

Stefanos Madagaskaris

Joined: Sep 09, 2008
Posts: 3
how can I initialize in a constructor this private instance variable?

private Map<String, Set<Integer>> variable;

I tried to use :

variable = new HashMap<String, TreeSet<Integer>>();

because I want each set to be ordered but I get an error.
Any ideas guys?
Thank you.
Jeff Langr
Ranch Hand

Joined: May 14, 2003
Posts: 762
You want to keep the bind types the same for the instantiated object:

but when you put elements into the map they can be of a concrete subtype:

If the client needs to know (doubtful in this case), or if you're worried about someone putting in a non-treeset instance, declare the map as binding to String and HashSet<Integer>.

[ September 09, 2008: Message edited by: Jeff Langr ]

Books: Agile Java, Modern C++ Programming with TDD, Essential Java Style, Agile in a Flash. Contributor, Clean Code.
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subject: private instance variable of Map type
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