CODEWITHSUNDEEP
javaandroidcollections
David
David

Reputation: 1246

Which Android / Java Collection should I use for sorted keys value pairs, and to return elements after given point

Lets say I have a list of keys that all contain an Object like this:

2, 4, 5, 9, 11

I need them to be ordered because I want to do something like:

function Object[] getObjectsAfter( int i ); 
// so 4 would result in an array of objects in the keys 5, 9 and 11

and

function Object[] getObjectsBefore( int i ); 
// so 4 would result in an array of objects in the keys 2

What collection is best to use in Android? I tried SparseArray and TreeMap, but I can't find a way to iterate from a certain point.

Upvotes: 2

Views: 269

Answers (2)

issathink
issathink

Reputation: 1230

You can use a SortedSet, it's a Set that further provides a total ordering on its elements. The elements are ordered using their natural ordering or by a Comparator typically provided at sorted set creation time (doc here).

Upvotes: 0

aioobe
aioobe

Reputation: 421130

If you...

  • ...need to have the elements ordered
  • ...don't want duplicates
  • ...want to be able to iterate from a specific point

you can use TreeSet.

Demo:

TreeSet<Integer> ints = new TreeSet<>(Arrays.asList(2,4,5,9,11));

System.out.println(ints.tailSet(4, false));  // [5, 9, 11]
System.out.println(ints.headSet(4, false));  // [2]

(If you want a Map you can use TreeMap with tailMap and headMap.)

Upvotes: 3

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