Re: Collection
Garg wrote:
but as Matt mentioned that the order deppends on the hashcode and
order they are inserted(i [sic] think it only depends on the hashcode).
Sort of, and it can change over the life of the Map.
I tried to implement
List <Map.Entry<K,V>> entryList = new ArrayList <Map.Entry<K,V>>
You do not need to mix Map and List in this way.
You should not embed the implementing type ("List") in the variable name. A
name that documents the /logical/ purpose is superior, and will not need
change as much if you refactor. Consider a name like "entries" for this one.
(myHashMap.entrySet());
Why make a list when you can iterate right over the Set? It's a lot of extra
copying and complexity for no gain.
K key = entryList.get(4).getKey();
V value = entryList.get(4).getValue();
But i [sic] am couldn't be able to compile this.
Would you be willing to show us an SSCCE
<http://www.physci.org/codes/sscce.html>
and copy-and-paste the error messages for us?
Comments based on the lack of information so far:
- You left out the generic types K and V in the declaration of your class that
has the "entryList" member. Thus K and V were not recognized types in the
compilation.
- You should declare your own wrapper type to hold the pair of values you want
to store, unless you truly want them to have a key-value relationship. The
purpose of a Map is to hold associations; using a Map as a List is overkill.
Instead, use a List from the get-go, and skip using a Map altogether.
- If, OTOH, you do need the associative lookup and only occasionally need to
loop through the entrySet, then just iterate over the entrySet. For most
implementations of Map, the order is irrelevant and will change between calls.
- The use of a Map to hold an association between keys and values is at
variance with the notion of ordering a list of value pairs by some intrinsic
order. For the latter, use a sorted
List <T extends Comparable<? super T>>
or List<T> sorted using a
Comparator<? super T>
or a SortedSet<T>. For the former where sort order really does matter, use a
SortedMap<T>. Matt Humphrey called your attention to the TreeMap
implementation. You should be able to simply iterate over that.
<http://java.sun.com/javase/6/docs/api/java/util/Collections.html#sort(java.util.List)>
<http://java.sun.com/javase/6/docs/api/java/util/Collections.html#sort(java.util.List,%20java.util.Comparator)>
<http://java.sun.com/javase/6/docs/api/java/util/SortedSet.html>
<http://java.sun.com/javase/6/docs/api/java/util/SortedMap.html>
- It is unlikely that you actually need both Mapness and sortedness.
--
Lew