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From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.java.programmer
Subject: Re: Working with an array of TreeSet
Date: Tue, 10 May 2016 23:22:09 +0200
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On Tuesday 10 May 2016 18:19 CEST, Marcel Mueller wrote:

> On 10.05.16 13.37, Cecil Westerhof wrote:
>> I would like to have an array of TreeSet<Integer>. But that is not
>> possible in Java.
>> So I use:
>> TreeSet<?>[] allNodes;
>
> Since Java uses ->type erasure the types TreeSet<?>[] and
> TreeSet<Integer>[] are identical. The strong typing is mainly a hint

I got a compiler error on TreeSet<Integer>[]. But ArrayList saved my
day.


>> And to add an Integer I use:
>> @SuppressWarnings("unchecked")
>> private static void addConnection(int from, int to) {
>> TreeSet<Integer> treeSet;
>>
>> treeSet = (TreeSet<Integer>) allNodes[from];
>> treeSet.add(to);
>> }
>>
>> Is this a correct way of doing this, or is there a better way?
>
> This is syntactically OK.
>
> The more interesting question is why you need an array of TreeSet.
> What is the semantic meaning of from? And what is the meaning of to?

I am mapping the connections of paths between nodes in a graph. From a
node to a node.


> It looks like an 1:n or m:n mapping. If the number of entries in one
> TreeSet is small a sorted list would perform better. Unfortunately
> such a type is missing from the Java class library. So you need to
> deal with an array or ArrayList and maintain the sort order by your
> own.

I prefer an algorithm that is clear. Only when there is a real problem
with performance I would sacrifice clearness of code.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof