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<TITLE>Creating a Hash Table (Java Developers Almanac Example)
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  <h3>e355. Creating a Hash Table</h3>

A hash table, or <font color="#0066ff"><i>map</i></font>, holds key/value pairs.


<pre>    // Create a hash table
    Map map = new HashMap();    // hash table
    map = new TreeMap();        // sorted map
    
    // Add key/value pairs to the map
    map.put(<font color="#0066ff"><i>"a"</i></font>, <font color="#0066ff"><i>new Integer(1)</i></font>);
    map.put(<font color="#0066ff"><i>"b"</i></font>, <font color="#0066ff"><i>new Integer(2)</i></font>);
    map.put(<font color="#0066ff"><i>"c"</i></font>, <font color="#0066ff"><i>new Integer(3)</i></font>);
    
    // Get number of entries in map
    int size = map.size();        // 2
    
    // Adding an entry whose key exists in the map causes
    // the new value to replace the old value
    Object oldValue = map.put(<font color="#0066ff"><i>"a"</i></font>, <font color="#0066ff"><i>new Integer(9)</i></font>);  // 1
    
    // Remove an entry from the map and return the value of the removed entry
    oldValue = map.remove(<font color="#0066ff"><i>"c"</i></font>);  // 3
    
    // Iterate over the keys in the map
    Iterator it = map.keySet().iterator();
    while (it.hasNext()) {
        // Get key
        Object key = it.next();
    }
    
    // Iterate over the values in the map
    it = map.values().iterator();
    while (it.hasNext()) {
        // Get value
        Object value = it.next();
    }
</pre>
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            &nbsp;<b>Related Examples</b></font></td>
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e356. <a class="eglink" href="coll_MapOrder.html?l=rel">
    Creating a Map That Retains Order-of-Insertion
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e357. <a class="eglink" href="coll_WeakMap.html?l=rel">
    Automatically Removing an Unreferenced Element from a Hash Table
</a>
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        See also: 
<a class="eglink" href="/egs/java.util/pkg.html?l=rel#Arrays">
    Arrays
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    Bits
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<a class="eglink" href="/egs/java.util/pkg.html?l=rel#Collections">
    Collections
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    Dates
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    Property Files
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<a class="eglink" href="/egs/java.util/pkg.html?l=rel#Sets">
    Sets
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    Sorted Collections
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    Time
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