Reputation: 3150

Setting size to TreeSet

Is there a way to give size limit to TreeSet in Java Collections as we do for arrays? for example in arrays we do,

anArray = new int[10];

Upvotes: 4

Answers (6)

Rémi Melisson

Reputation: 2773

Here is an implementation of BoundedTreeSet in Apache Solr, which keeps the biggest values when trying to insert into a "full" set :

http://lucene.apache.org/solr/4_6_0/solr-core/org/apache/solr/util/BoundedTreeSet.html

Maven artifact available here :

<dependency>
   <groupId>org.apache.solr</groupId>
   <artifactId>solr-core</artifactId>
   <version>4.6.0</version>
</dependency>

Upvotes: 2

dMb

Reputation: 9337

The closest you can come to an existing collection with capacity limits is a BlockingQueue. When adding items to the queue, you can specify a zero second (or very small) blocking timeout, so that an exception is thrown when the capacity is exceeded. For more details, see BlockingQueue.offer()

Upvotes: 0

Óscar López

Reputation: 236014

None of TreeSet's constructors specifies an initial size, it grows when elements are added. And there's no way to limit the maximum size of the data structure. Every time you add() a new element, you'd need to manually check if it has exceeded the maximum size allowed. You can specify this behavior by implementing a subclass that extends from TreeSet and overriding add(), addAll(), and the two constructors that receive a Collection as a parameter.

Upvotes: 2

Jon Newmuis

Reputation: 26502

You can always make your own implementation. Here is an example to get you started; you may find that you wish to tweak it accordingly:

public class BoundedTreeSet<E> extends TreeSet<E> {

    private final int limit;

    public BoundedTreeSet(final int limit) {
        super();
        this.limit = limit;
    }

    public BoundedTreeSet(final int limit, final Collection<? extends E> c) {
        super(c);
        this.limit = limit;
    }

    public BoundedTreeSet(final int limit, final Comparator<? super E> comparator) {
        super(comparator);
        this.limit = limit;
    }

    public BoundedTreeSet(final int limit, final SortedSet<E> s) {
        super(s);
        this.limit = limit;
    }

    @Override
    public boolean add(final E e) {
        if (size() >= limit) {
            return false;
        }

        return super.add(e);
    }

    @Override
    public boolean addAll(Collection<? extends E> c) {
        if (size() + c.size() >= limit) {
            return false;
        }

        return super.addAll(c);
    }
}

Upvotes: 2