Re: static hashtable with conent?

From:
Owen Jacobson <angrybaldguy@gmail.com>
Newsgroups:
comp.lang.java.programmer
Date:
Sun, 25 Nov 2007 03:15:26 GMT
Message-ID:
<200711241915268930-angrybaldguy@gmailcom>
On 2007-11-24 17:36:16 -0800, "Mike Schilling"
<mscottschilling@hotmail.com> said:

Owen Jacobson wrote:

On 2007-11-24 11:57:48 -0800, "Mike Schilling"
<mscottschilling@hotmail.com> said:

Kevin wrote:

Did not find out the answer after some google:

how can we create a static hashtable with some initial values there?

static Hashtable ht = new Hasthable();

will only create a empty one. Suppose I want to put some Integer
values as keys and values of this hashtable, how can I do that?


Use a static init block (And use a HashMap; Hashtable is obsolete)

static Map map;
static
{
map = new HashMap();
map.put("if", IF_TOKEN);
map.put("else", ELSE_TOKEN);
...
}


There is a trick for emulating (sort of) map literals in Java that
might be useful here:

static Map<String, Whatever> map = new HashMap<String, Whatever> () {{
put ("if", IF_TOKEN);
put ("else", ELSE_TOKEN);
// ...
}};

It does have the cost of requiring one more class to be loaded. It
will also confuse reflection-based code that expects the 'map' field
to _be_ a specific subtype rather than _assignable to_ a specific
subtype. OTOH, I find both of those concerns are rarely important in
my own code.


It'll also confuse the hell out of anyone who's never seen it before. I got
it eventually, but it's not really obvious that "{{" introduces an init
block in an anonymous class.


*grin*

That's about what my initial reaction to it was. It's also nowhere
near as elegant as Perl or Python's dictionary literals.

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