Difference Between Hashtable and Synchronized Map in Java
Feb 07, 2025 am 11:45 AMThis article explores the key distinctions between Java's Hashtable
and SynchronizedMap
. A Hashtable
efficiently maps keys to values using an array of slots accessed via index calculation, providing fast data retrieval. Conversely, a SynchronizedMap
synchronizes a map to ensure thread safety, preventing concurrent access issues. Crucially, SynchronizedMap
does not permit null values.
Input Example
<code>[ARB, RDD, KOL, DHKA]</code>
Output Example
<code>Hashtable Insertion Order: [ARB, RDD, KOL, DHKA] SynchronizedMap Insertion Order: [ARB, RDD, DHKA, KOL]</code>
Methodology
The comparison involves analyzing insertion order using ArrayLists and Sets to track element placement. A timed loop is used for iterative processing.
Algorithm Steps:
- Initialize input/output streams.
- Import necessary classes and define functions.
- Create a public class.
- Define functions for insertion order tracking.
- Populate an ArrayList with input data.
- Utilize Sets (e.g., LinkedHashSet for insertion order preservation) to manage data.
- Print insertion order for both
Hashtable
andSynchronizedMap
. - Implement a timed loop for iterative processing.
- Output the results.
Syntax Example (Illustrative)
The following snippet demonstrates the use of TreeSet
, IdentityHashMap
, and other relevant classes to illustrate the concepts. Note that this is a simplified example and not a complete implementation of the algorithm described above.
TreeSet<Integer> stTree = new TreeSet<>(); stTree.add(4); stTree.add(5); stTree.add(6); stTree.add(8); stTree.add(4); IdentityHashMap<Integer, String> ihmap = new IdentityHashMap<>(); ihmap.put(10, "ARB"); ihmap.put(20, "RDD"); ihmap.put(30, "ARBRDD"); ihmap.put(40, "KOLDHKA"); ihmap.put(50, "You"); System.out.println("IdentityHashMap size: " + ihmap.size()); System.out.println("Initial IdentityHashMap: " + ihmap); Hashtable<Integer, String> table = new Hashtable<>(); table.put(1, "X"); table.put(2, "Y"); table.put(3, "Z"); table.put(4, "A"); for (Map.Entry<Integer, String> m : table.entrySet()) { Iterator<Map.Entry<Integer, String>> itr = ihmap.entrySet().iterator(); while (itr.hasNext()) { IdentityHashMap.Entry<Integer, String> entry = itr.next(); TreeMap<Integer, Integer> maptree = new TreeMap<>(); maptree.put(2, 5); maptree.put(3, 6); maptree.put(4, 6); maptree.put(2, 3); } }
Hashtable
vs. SynchronizedMap
Comparison
Feature |
|
?> | ||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Data Structure | Uses a hash table for key-value storage. | Wraps an existing map for thread safety. | ||||||||||||||||||
Element Order | Arbitrary | Retains the original map's insertion order. | ||||||||||||||||||
Thread Safety | Inherently synchronized (can be slow). | Synchronized using Collections.synchronizedMap() |
||||||||||||||||||
Performance | Can be slower due to inherent synchronization. | Performance overhead due to synchronization. | ||||||||||||||||||
Null Values | Does not allow null keys or values. | Inherits null value handling from wrapped map. |
Hashtable
provides built-in thread safety but might suffer performance penalties. SynchronizedMap
offers a more flexible approach, allowing you to synchronize any map implementation, but it introduces a performance overhead. Hashtable
is generally considered a legacy class, and SynchronizedMap
or concurrent collections (like ConcurrentHashMap
) are preferred for modern Java development.
Object-Level Synchronization
Object-level synchronization, using the synchronized
keyword, ensures that only one thread can access a specific object's methods at a time.
Example using Object-Level Synchronization
This example demonstrates synchronizing a HashMap
using Collections.synchronizedMap()
.
<code>[ARB, RDD, KOL, DHKA]</code>
Conclusion
Choosing between Hashtable
and SynchronizedMap
depends on your specific needs. For thread safety in modern Java applications, consider using ConcurrentHashMap
for better performance compared to SynchronizedMap
or Hashtable
. Hashtable
is generally discouraged for new code.
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