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| Java Collection Framework - HashSet & TreeSet Classes |
The Collection Framework provides
two general purpose implementations
often Set interface, HashSet and TreeSet.
More often than not you will use a
HashSet for storing your duplicate-free
collection. For efficiency objects
added to a HashSet need to implement
the hashCode() method in a manner
that properly distributes the hash
codes. While most system classes override
the default hashCode() implementation
of the Object, when creating your
own class to add to a HashSet remember
to override hashCode().
The
TreeSet implementations useful when
you need to extract elements from
a collection in a sorted manner. It
is generally faster to add elements
to the HasSet then convert the collection
to a TreeeSet for sorted traversal.
To optimize HashSet space usage ,
you can tune initial capacity and
load factor. TreeSet has no tuning
options, as the tree is always balanced,
ensuring log(n0 performance for insertions,
deletions and queries.
Example
import
java.util.*;
public class HashTreeSetEx{ |
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public
static void main (String args[]){ |
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Set
set = new HashSet(){
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set.add("one");
set.add("two");
set.add("three");
set.add("four");
set.add("one");
System.out.println(set);
Set sortedSet= new TreeSet(set);
System.out.println(SortedSet); |
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} |
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} |
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| } |
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The
program produces the following output.
The duplicate entry is olypresent
once and the second line outputs sorted
[one, two, three, four]
[four, one, three, two]
Note that these implementation is
not synchronized. If multiple threads
access a set concurrently, and at
least one of the threads modifies
the set, it must be synchronized externally.
This is typically accomplished by
synchronizing on some object that
naturally encapsulates the set. If
no such object exists, the set should
be "wrapped" using the Collections.synchronizedSet
method. This is best done at creation
time, to prevent accidental unsynchronized
access to the set:
Set
s = Collections.synchronizedSet(new
HashSet(...));
SortedSet
s = Collections.synchronizedSortedSet(new
TreeSet(...));
Explore the other Interface and Classes
of Java Collection Framework
Collection
Interface
Iterator
Interface
Set
Interface
List
Interface
ListIterator
Interface
Map
Interface
SortedSet
Interface
SortedMap
Interface
HashSet
& TreeSet Classes
ArrayList
& LinkedList Classes
HashMap
& Treemap Classes
Vector
and Stack Classes
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