<h1 id="map">Map<a aria-hidden="true" class="anchor-heading icon-link" href="#map"></a></h1>
<ul>
<li>To represent group of objects as key value pairs</li>
<li>NOT a child interface of <a href="/cs/notes/rpb0p7ld8g30mdscf1r32re">Collection Interface</a></li>
<li>Therefore, strictly speaking, <a href="/cs/notes/rpb0p7ld8g30mdscf1r32re">Collection Interface</a> is NOT root interface of Collection framework</li>
<li>Duplicates
<ul>
<li>Keys - <a href="/cs/notes/erabl4efwn49ad1hyh9q9xo">Duplicates - NOT Allowed</a></li>
<li>Values - <a href="/cs/notes/esvk57cujir0xgnugroobcg">Duplicates - Allowed</a></li>
</ul>
</li>
</ul>
<h2 id="hashmap-vs-hashtable"><a href="/cs/notes/2flikwueaimsj1naahg6gn2">HashMap</a> vs <a href="/cs/notes/gu1ozy25u42r56u3nsuucww">Hashtable</a><a aria-hidden="true" class="anchor-heading icon-link" href="#hashmap-vs-hashtable"></a></h2>
<div class="table-responsive">





























<table><thead><tr><th></th><th>HashMap</th><th>Hashtable</th></tr></thead><tbody><tr><td>Introduced in</td><td>1.2</td><td>1.0</td></tr><tr><td>Thread Safety</td><td>Not thread safe (not synchronized) => works with single thread</td><td>Thread safe (synchronized) => works with multiple threads</td></tr><tr><td>Speed</td><td>Faster</td><td>Slower</td></tr><tr><td>Null key</td><td>One null key allowed</td><td>Null key not allowed</td></tr></tbody></table></div>
<p>Child classes/interfaces:</p>
<ul>
<li><a href="/cs/notes/2flikwueaimsj1naahg6gn2">HashMap</a></li>
<li><a href="/cs/notes/b63mj2mkjzvz4ridttd0ge9">WeakHashMap</a></li>
<li><a href="/cs/notes/wlftnmp7thzpvca4ocbbxsf">IdentityHashMap</a></li>
<li><a href="/cs/notes/4cyorq5w2fbmxmys9kowugd">SortedMap</a> (I)</li>
<li><a href="/cs/notes/gu1ozy25u42r56u3nsuucww">Hashtable</a></li>
</ul>
<hr>
<strong>Children</strong>
<ol>
<li><a href="/cs/notes/2flikwueaimsj1naahg6gn2">HashMap</a></li>
<li><a href="/cs/notes/gu1ozy25u42r56u3nsuucww">Hashtable</a></li>
<li><a href="/cs/notes/wlftnmp7thzpvca4ocbbxsf">IdentityHashMap</a></li>
<li><a href="/cs/notes/4cyorq5w2fbmxmys9kowugd">SortedMap</a></li>
<li><a href="/cs/notes/b63mj2mkjzvz4ridttd0ge9">WeakHashMap</a></li>
</ol>
<hr>
<strong>Backlinks</strong>
<ul>
<li><a href="/cs/notes/fi3xznhjsf8ezkolih7torp">Collection Frameworks Cheatsheet (cs)</a></li>
<li><a href="/cs/notes/2flikwueaimsj1naahg6gn2">HashMap (cs)</a></li>
<li><a href="/cs/notes/gu1ozy25u42r56u3nsuucww">Hashtable (cs)</a></li>
<li><a href="/cs/notes/4cyorq5w2fbmxmys9kowugd">SortedMap (cs)</a></li>
</ul>



These notes are arranged into the below topics:

- AI (Sorry this is on the top, list is alphabetic)
- [[arch]]
- Data
- Execution
- Languages
- Semantics
- [[paradigm]]
- Philosophy
- Dev
- Tools
- Type Theory

## References

- Hierarchy inpiration - [Map of Computer Science](https://www.flickr.com/photos/95869671@N08/36231833334/in/photostream/lightbox/)

	HashMap	Hashtable
Introduced in	1.2	1.0
Thread Safety	Not thread safe (not synchronized) => works with single thread	Thread safe (synchronized) => works with multiple threads
Speed	Faster	Slower
Null key	One null key allowed	Null key not allowed

Map

HashMap vs Hashtable