HashMap
 

Hello

I have HashMap with two identical keys, but different values. If do a
"get(key name)" on the HashMap Object I don't get both values. I know this
how it is supposed to work. The question - is there any data structure in java
which will return values for identical keys ?

-sanjay

Re: HashMap
 

Sanjay Kumar wrote

> I have HashMap with two identical keys, but different values. If do a
> "get(key name)" on the HashMap Object I don't get both values. I know this
> how it is supposed to work. The question - is there any data structure in
java
> which will return values for identical keys ?

The Map interface do not directly support implementations that map a key to
multiple values. However, since values can be any object you like, including
other collections, you can perhaps use another Collection inside your Map,
like in the following example:

public class MyMap {

private Map map = new HashMap();

public void add(Object key, Object value) {
Collection values = get(key);
if (values == null) {
values = new HashSet(); // use whatever collection makes sense
map.put(key,values);
}
values.add(value);
}

public void remove(Object key, Object value) {
Collection values = get(key);
if (values == null) return;
values.remove(value);
if (values.isEmpty()) {
map.remove(key);
}
}

public Collection get(Object key) {
return (Collection) map.get(key);
}

// delegate to other map methods as needed ...
}


So, with

MyMap myMap = new MyMap();
myMap.add(key,value1);
myMap.add(key,value2);

you can iterate now over the elements for key by doing

Iterator i = myMap.get(key).elements();
while (i.hasNext()) {
Object myValue = i.next();
}



--
Filip Larsen

Re: HashMap
 

Thanks for all the ideas !!

-sanjay

nd81@hotmail.com (Sanjay Kumar) wrote in message news:<99793c86.0307040702.17baf8e0@posting.google. com>...
> Hello
>
> I have HashMap with two identical keys, but different values. If do a
> "get(key name)" on the HashMap Object I don't get both values. I know this
> how it is supposed to work. The question - is there any data structure in java
> which will return values for identical keys ?
>
> -sanjay