How to give the static value to HashMap?

问题

I have HashMap like:

static HashMap<String,ArrayList<Media>> mediaListWithCategory=new HashMap<String,ArrayList<Media>>();

I have value like:

January:
   -Sunday
   -Monday
Februsry:
   -Saturday
   -Sunday
   -Thursday
March:
   -Monday
   -Tuesday
   -Wednesday

How can I statically assign these values when defining the hash map?

回答1:

You can populate it in a static block:

static {
   map.put("January", Arrays.asList(new Media("Sunday"), new Media("Monday")));
}

(You should prefer interface to concrete classes. define your type as Map<String, List<Media>>)

回答2:

Use a static block:

static {
  mediaListWithCategory.put(youKey, yourValue);
}

回答3:

A variant of this may be more succinct:

static HashMap<String, ArrayList<String>> map = new HashMap<String, ArrayList<String>>() {{
    put("January", new ArrayList<String>() {{
        add("Sunday");
        add("Monday");
      }});
    put("Februsry" /* sic. */, new ArrayList<String>() {{
        add("Saturday");
        add("Sunday");
        add("Thursday");
      }});
    put("March", new ArrayList<String>() {{
        add("Monday");
        add("Tuesday");
        add("Wednesday");
      }});
}};

See Double Brace Initialisation for discussion.

来源：https://stackoverflow.com/questions/8211784/how-to-give-the-static-value-to-hashmap