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copied!<p>A <a href="http://java.sun.com/javase/6/docs/api/java/util/HashMap.html" rel="noreferrer"><code>HashMap</code></a> (and its legacy predecesor <a href="http://java.sun.com/javase/6/docs/api/java/util/Hashtable.html" rel="noreferrer"><code>Hashtable</code></a>) is by nature unordered. Even if you sort it, it will remain unordered. If you want to maintain insertion order, then use <a href="http://java.sun.com/javase/6/docs/api/java/util/LinkedHashMap.html" rel="noreferrer"><code>LinkedHashMap</code></a> instead. If you want an automatic sort on <strong>keys</strong>, regardless of insertion order, then use <a href="http://java.sun.com/javase/6/docs/api/java/util/SortedMap.html" rel="noreferrer"><code>SortedMap</code></a> instead.</p> <p>If you want to sort a <code>Map</code> on <strong>values</strong>, then you basically need to put the key/value pairs in another kind of a sortable data structure, e.g. <code>List<Entry<K, V>></code>, then sort it using <code>Collections#sort()</code> with help of a <code>Compatator<Entry<K, V>></code> and finally repopulate a <code>LinkedHashMap</code> with it (not a <code>HashMap</code> or you will lose the ordering again).</p> <p>Here's a basic example (leaving obvious runtime exception handling aside):</p> <pre><code>// Prepare. Map<String, String> map = new HashMap<String, String>(); map.put("foo", "bar"); map.put("bar", "waa"); map.put("waa", "foo"); System.out.println(map); // My JVM shows {waa=foo, foo=bar, bar=waa} // Get entries and sort them. List<Entry<String, String>> entries = new ArrayList<Entry<String, String>>(map.entrySet()); Collections.sort(entries, new Comparator<Entry<String, String>>() { public int compare(Entry<String, String> e1, Entry<String, String> e2) { return e1.getValue().compareTo(e2.getValue()); } }); // Put entries back in an ordered map. Map<String, String> orderedMap = new LinkedHashMap<String, String>(); for (Entry<String, String> entry : entries) { orderedMap.put(entry.getKey(), entry.getValue()); } System.out.println(orderedMap); // {foo=bar, waa=foo, bar=waa} </code></pre> <p>To sort it <strong>descencing</strong>, use the following <code>Comparator</code>. Basically just swap the entries to compare:</p> <pre><code>Collections.sort(entries, new Comparator<Entry<String, String>>() { public int compare(Entry<String, String> e1, Entry<String, String> e2) { return e2.getValue().compareTo(e1.getValue()); // Sorts descending. } }); </code></pre>

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