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<ul>
<li>A <b>Hashtable </b>is an array of list.Each list is known as a bucket.The position of bucket is identified by calling the <b>hashcode()</b> method. A <b> Hashtable </b>contains values based on the key. It implements the Map interface and extends Dictionary class.</li>
<li>It contains only unique elements.</li>
<li>It may have not have any null key or value.</li>
<li>It is synchronized.</li>
</ul>
<p>Like <b>HashMap</b>, <b>Hashtable </b>stores key/value pairs in a hash table. When using a <b>Hashtable</b>, you specify an object that is used as a key, and the value that you want linked to that key. The key is then hashed, and the resulting hash code is used as the index at which the value is stored within the table.</p>
<p> <b>Constructors:</b></p>
<p></p>
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<p>The <b>Hashtable </b>defines four constructors. The first version is the default constructor:</p>
<pre class="highlight" name="code">Hashtable( ) 
</pre>
<p>The second version creates a hash table that has an initial size specified by size:</p>
<pre class="highlight" name="code">Hashtable(int size) 
</pre>
<p>The third version creates a hash table that has an initial size specified by size and a fill ratio specified by <b>fillRatio</b>.</p>
<p> This ratio must be between 0.0 and 1.0, and it determines how full the hash table can be before it is resized upward.</p>
<pre class="highlight" name="code">Hashtable(int size, float fillRatio) 
</pre>
<p>The fourth version creates a hash table that is initialized with the elements in m.</p>
<p> The capacity of the hash table is set to twice the number of elements in m. The default load factor of 0.75 is used.</p>
<pre class="highlight" name="code">Hashtable(Map m) 
</pre>
<p><b>Methods:</b><br />
Apart from the methods defined by <b>Map </b>interface, <b>Hashtable </b>defines following methods:</p>
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<th style="background-color: #eeeeee; border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px; text-align: left;">SN</th>
<th style="background-color: #eeeeee; border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px; text-align: left;">Methods with Description</th>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">1</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">void clear( )</b><br />
Resets and empties the hash table.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">2</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">Object clone( )</b><br />
Returns a duplicate of the invoking object.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">3</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">boolean contains(Object value)</b><br />
Returns true if some value equal to value exists within the hash table. Returns false if the value isn&#8217;t found.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">4</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">boolean containsKey(Object key)</b><br />
Returns true if some key equal to key exists within the hash table. Returns false if the key isn&#8217;t found.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">5</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">boolean containsValue(Object value)</b><br />
Returns true if some value equal to value exists within the hash table. Returns false if the value isn&#8217;t found.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">6</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">Enumeration elements( )</b><br />
Returns an enumeration of the values contained in the hash table.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">7</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">Object get(Object key)</b><br />
Returns the object that contains the value associated with key. If key is not in the hash table, a null object is returned.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">8</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">boolean isEmpty( )</b><br />
Returns true if the hash table is empty; returns false if it contains at least one key.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">9</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">Enumeration keys( )</b><br />
Returns an enumeration of the keys contained in the hash table.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">10</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">Object put(Object key, Object value)</b><br />
Inserts a key and a value into the hash table. Returns null if key isn&#8217;t already in the hash table; returns the previous value associated with key if key is already in the hash table.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">11</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">void rehash( )</b><br />
Increases the size of the hash table and rehashes all of its keys.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">12</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">Object remove(Object key)</b><br />
Removes key and its value. Returns the value associated with key. If key is not in the hash table, a null object is returned.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">13</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">int size( )</b><br />
Returns the number of entries in the hash table.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">14</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">String toString( )</b><br />
Returns the string equivalent of a hash table.</td>
</tr>
</tbody>
</table>
<p>
<b>Example of <i>Hashtable</i>:</b></p>
<pre class="highlight" name="code">import java.util.*; 
class Simple{ 
 public static void main(String args[]){ 
 
 Hashtable hm = new Hashtable(); 
 
 hm.put(100,"Dinesh"); 
 hm.put(102,"Sweety"); 
 hm.put(101,"Ankit"); 
 hm.put(103,"Nimmo"); 
 
 Set set = hm.entrySet(); 
 Iterator itr = set.iterator(); 
 
 while(itr.hasNext()){ 
 Map.Entry m=(Map.Entry)itr.next(); 
 System.out.println(m.getKey()+" "+m.getValue()); 
 } 
 } 
} 
</pre>
<div style="background-color: #ff99cc;"><b>Output:</b><br />
103 Rahul<br />
102 Ravi<br />
101 Vijay<br />
100 Amit</div>
<div style="background-color: #f2f9fc; border-radius: 3px; border: 1px solid #c9e6f2; line-height: 1.45; padding: 16px;">
<b>Java Collections Tutorial</b></p>
<ol style="text-align: left;">
<li><b><a href="https://dineshonjava.com/arraylist-class-in-java-collection/">ArrayList class</a></b></li>
<li><b><a href="https://dineshonjava.com/linkedlist-class-in-collection/">LinkedList class</a></b></li>
<li><b><a href="https://dineshonjava.com/listiterator-interface-in-collection/">ListIterator interface</a></b></li>
<li><b><a href="https://dineshonjava.com/hashset-class-in-collection/">HashSet class</a></b></li>
<li><b><a href="https://dineshonjava.com/linkedhashset-class-in-collection/">LinkedHashSet class</a></b></li>
<li><b><a href="https://dineshonjava.com/treeset-classin-collection/">TreeSet class</a></b></li>
<li><b><a href="https://dineshonjava.com/difference-between-hashset-and-treeset/">Difference between TreeSet &; HashSet</a></b></li>
<li><b><a href="https://dineshonjava.com/map-interface-in-collection/">Map interface</a></b></li>
<li><b><a href="https://dineshonjava.com/hashmap-class-in-collection-framework/">HashMap class</a></b></li>
<li><b><a href="https://dineshonjava.com/how-does-java-hashmap-work-internally/">How does work HashMap?</a> </b></li>
<li><b><a href="https://dineshonjava.com/difference-between-treemap-vs-hashmap/">Difference between TreeMap vs HashMap</a></b></li>
<li><b><a href="https://dineshonjava.com/linkedhashmap-class-in-collection/">LinkedHashMap class</a></b></li>
<li><b><a href="https://dineshonjava.com/treemap-class-in-collection-framework/">TreeMap class</a></b></li>
<li><b><a href="https://dineshonjava.com/difference-between-hashmap-and/">Difference between HashMap and HashTable in Java</a></b></li>
<li><b><a href="https://dineshonjava.com/sorting-in-collection-framework/">Sorting</a></b></li>
<li><b><a href="https://dineshonjava.com/java-comparable-and-comparator/">Comparable interface</a></b></li>
</ol>
</div>
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