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    <p>It is not possible to sort a HashMap. If you need a sorted map take a look at <a href="http://docs.oracle.com/javase/7/docs/api/java/util/TreeMap.html" rel="nofollow"><code>TreeMap</code></a>.</p> <p>What about adding the rating value to the <code>Movie</code> class and let it implement <code>Comparable</code>?</p> <pre><code>public class Movie implements Comparable&lt;Movie&gt; { private Float rating; public Movie(Float rating) { this.rating = rating; } public Float getRating() { return rating; } public int compareTo(Movie param) { return param.getRating().compareTo(rating); } @Override public String toString() { return String.valueOf(rating); } } </code></pre> <p>Then you can use your <code>Movie</code> class like this:</p> <pre><code>public static void main(String[] args) { Set&lt;Movie&gt; movies = new HashSet&lt;Movie&gt;(); movies.add(new Movie(0.6f)); movies.add(new Movie(0.5f)); movies.add(new Movie(0.7f)); movies.add(new Movie(0.2f)); // Movie.class has to implement Comparable System.out.println("First option:"); List&lt;Movie&gt; list = new ArrayList&lt;Movie&gt;(movies); Collections.sort(list); printMovies(list); // Works without implementing Comparable in Movie.class System.out.println("\nSecond option:"); List&lt;Movie&gt; secondList = new ArrayList&lt;Movie&gt;(movies); Collections.sort(secondList, new Comparator&lt;Movie&gt;() { public int compare(Movie movie1, Movie movie2) { return movie2.getRating().compareTo(movie1.getRating()); } }); printMovies(secondList); } private static void printMovies(List&lt;Movie&gt; list) { for (Movie movie : list) { System.out.println(movie); } } </code></pre> <p>Output:</p> <pre><code>First option: 0.7 0.6 0.5 0.2 Second option: 0.7 0.6 0.5 0.2 </code></pre> <p>If you always want to sort the movies in the same way (from best to worse), I would choose the first option. If you always need different sort algorithms I would choose the second option, but even if your <code>Movie</code> class implements <code>Comparable</code> you can always provide a different <code>Comparator</code> as shown in the example.</p>
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    1. USMatthias Herlitzius
    1. USMatthias Herlitzius
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    1. COWhile this is an ok solution, I think it makes the code easier to read if you use Comperator rather than Compareable in situations like this. When I read Collections.sort(list) I will often assume its sorted on title or similar, not on rating, but if I instead read Collections.sort(list, new Movie.RatingComperator()) I can see right away that it will be sorted by rating and not something else.
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    2. COI updated my example to include your suggestion.
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