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    <p>A <code>TreeMap</code> is a <a href="http://java.sun.com/javase/6/docs/api/java/util/SortedMap.html" rel="nofollow noreferrer"><code>SortedMap</code></a>, which sorts by keys. The way you were using it, you have <code>String</code> keys, and its natural ordering is lexicographical, where <code>"11" &lt; "2"</code>.</p> <p>Here's an illustration using <code>List</code> to simplify:</p> <pre><code>List&lt;String&gt; list = new ArrayList&lt;String&gt;( Arrays.asList("2", "1", "11", "b", "a", "aa") ); Collections.sort(list); System.out.println(list); // prints "[1, 11, 2, a, aa, b]" </code></pre> <p>Note the analogy between <code>1, 11, 2</code> and <code>a, aa, b</code>. This is precisely what lexicographical ordering mandates. In a dictionary, you expect <code>aa</code> to appear before <code>b</code>. Similary, in this ordering, you expect <code>11</code> to appear before <code>2</code>.</p> <h3>See also</h3> <ul> <li><a href="http://en.wikipedia.org/wiki/Lexicographical_order" rel="nofollow noreferrer">Wikipedia/Lexicographical order</a></li> </ul> <hr> <p>If you need to compare them as <code>Integer</code>, use a custom <code>Comparator&lt;String&gt;</code>:</p> <pre><code>Comparator&lt;String&gt; stringAsInteger = new Comparator&lt;String&gt;() { @Override public int compare(String s1, String s2) { return Integer.valueOf(s1).compareTo(Integer.valueOf(s2)); } }; List&lt;String&gt; list = new ArrayList&lt;String&gt;( Arrays.asList("2", "1", "10", "007") ); Collections.sort(list, stringAsInteger); System.out.println(list); // prints "[1, 2, 007, 10]" SortedMap&lt;String, String&gt; map = new TreeMap&lt;String, String&gt;(stringAsInteger); map.put("2", "Two"); map.put("1", "One"); map.put("10", "Ten"); map.put("12", "Twelve"); map.put("7", "Seven"); System.out.println(map); // prints "{1=One, 2=Two, 7=Seven, 10=Ten, 12=Twelve}" </code></pre> <h3>API links</h3> <ul> <li><a href="http://java.sun.com/javase/6/docs/api/java/util/Comparator.html" rel="nofollow noreferrer"><code>java.util.Comparator</code></a></li> <li><a href="http://java.sun.com/javase/6/docs/api/java/util/Collections.html#sort%28java.util.List%29" rel="nofollow noreferrer"><code>Collections.sort</code></a> -- there are 2 overloads</li> </ul> <h3>Related questions</h3> <p>On <code>Comparator</code> and <code>Comparable</code></p> <ul> <li><a href="https://stackoverflow.com/questions/2266827/when-to-use-comparable-vs-comparator">When to use Comparable vs Comparator</a></li> <li><a href="https://stackoverflow.com/questions/420223/difference-between-compare-and-compareto">difference between compare() and compareTo()</a></li> <li><a href="https://stackoverflow.com/questions/2858628/comparable-and-comparator-contract-with-regards-to-null">Comparable and Comparator contract with regards to null</a></li> <li><a href="https://stackoverflow.com/questions/2892947/why-does-the-java-collections-framework-offer-two-different-ways-to-sort/">Why does the Java Collections Framework offer two different ways to sort?</a></li> </ul> <p>On sorting <code>Map</code> by values</p> <ul> <li><a href="https://stackoverflow.com/questions/2864840/treemap-sort-by-value">TreeMap sort by value</a></li> <li><a href="https://stackoverflow.com/questions/109383/how-to-sort-a-mapkey-value-on-the-values-in-java">How to sort a Map on the values in Java?</a></li> </ul> <hr> <h3>On raw types</h3> <p><em>Effective Java 2nd Edition, Item 23: Don't use raw types in new code</em></p> <h3>Related questions</h3> <ul> <li><a href="https://stackoverflow.com/questions/2770321/what-is-a-raw-type-and-why-shouldnt-we-use-it">What is a raw type and why shouldn’t we use it?</a></li> </ul>
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    1. CONear the top you show this style of syntax: `List<String> list = new ArrayList<String>( Arrays.asList("a", "b", "c") );` I've also used this syntax `List<String> list = Arrays.asList( new String[]{"a", "b", "c"} );` Curious if you had any comments for pro/con on either way? I had came to my syntax by trial and error, so not attached to it.
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