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POJava - List sorting doesn't work
 

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  1. POJava - List sorting doesn't work
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    <p>I'm trying to sort a hashmap's by sorting it's keys but it doesn't work. The sorting criteria is given by the length of a list that is the hashmap's value. See code below with some unit test.</p> <p>Class:</p> <pre><code>package com.fabri.interpreter.util; import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.HashMap; import java.util.List; import com.fabri.interpreter.VerbExpr; import com.fabri.interpreter.ObjectExpr; public class Environment { private HashMap&lt;VerbExpr, List&lt;ObjectExpr&gt;&gt; map = new HashMap&lt;VerbExpr, List&lt;ObjectExpr&gt;&gt;(); public List&lt;ObjectExpr&gt; eval(VerbExpr verb) { return map.get(verb); } public void put(VerbExpr verb, ObjectExpr words) { List&lt;ObjectExpr&gt; values; if(map.get(verb) == null) values = new ArrayList&lt;ObjectExpr&gt;(); else values = map.get(verb); values.add(words); map.put(verb, values); } public HashMap&lt;VerbExpr, List&lt;ObjectExpr&gt;&gt; getMap() { return map; } public void sort() { List&lt;VerbExpr&gt; keys = new ArrayList&lt;VerbExpr&gt;(map.keySet()); Collections.sort(keys, new Comparator&lt;VerbExpr&gt;() { @Override public int compare(VerbExpr verb1, VerbExpr verb2) { return map.get(verb1).size()-map.get(verb2).size(); } }); HashMap&lt;VerbExpr, List&lt;ObjectExpr&gt;&gt; sortedMap = new HashMap&lt;VerbExpr, List&lt;ObjectExpr&gt;&gt;(); for(VerbExpr verb : keys) { sortedMap.put(verb, map.get(verb)); } map = sortedMap; } } </code></pre> <p>Testing class:</p> <pre><code>package com.fabri.interpreter.util; import static org.junit.Assert.assertTrue; import java.util.ArrayList; import java.util.List; import org.junit.Before; import org.junit.Test; import com.fabri.interpreter.ObjectExpr; import com.fabri.interpreter.VerbExpr; import com.fabri.interpreter.WordExpr; public class TestEnvironment { private Object[] verbExprs; @Before public void setUp() { Environment env = new Environment(); List&lt;WordExpr&gt; words1 = new ArrayList&lt;WordExpr&gt;(); words1.add(new WordExpr("american")); words1.add(new WordExpr("italian")); env.put(new VerbExpr("was"), new ObjectExpr(words1)); List&lt;WordExpr&gt; words2 = new ArrayList&lt;WordExpr&gt;(); words2.add(new WordExpr("zero")); words2.add(new WordExpr("one")); words2.add(new WordExpr("two")); env.put(new VerbExpr("is"), new ObjectExpr(words2)); env.sort(); verbExprs = env.getMap().keySet().toArray(); } @Test public void testEnvironment() { assertTrue(((VerbExpr)verbExprs[0]).equals("is")); assertTrue(((VerbExpr)verbExprs[1]).equals("was")); } } </code></pre>
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