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POCompare two Java Collections using Comparator instead of equals()
 

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    <h1>Problem Statement</h1> <p>I have two Collections of the same type of object that I want to compare. In this case, I want to compare them based on an attribute that does not factor into <code>equals()</code> for the Objects. In my example, I'm using ranked collections of Names for instance:</p> <pre><code>public class Name { private String name; private int weightedRank; //getters &amp; setters @Override public boolean equals(Object obj) { return this.name.equals(obj.name); //Naive implementation just to show //equals is based on the name field. } } </code></pre> <p>I want to compare the two Collections to assert that, for position <code>i</code> in each Collection, the <code>weightedRank</code> of each Name at that position is the same value. I did some Googling but didn't find a suitable method in Commons Collections or any other API so I came up with the following:</p> <pre><code>public &lt;T&gt; boolean comparatorEquals(Collection&lt;T&gt; col1, Collection&lt;T&gt; col2, Comparator&lt;T&gt; c) { if (col1 == null) return col2 == null; if (col2 == null) return false; if (col1.size() != col2.size()) return false; Iterator&lt;T&gt; i1 = col1.iterator(), i2 = col2.iterator(); while(i1.hasNext() &amp;&amp; i2.hasNext()) { if (c.compare(i1.next(), i2.next()) != 0) { return false; } } return true; } </code></pre> <h1>Question</h1> <p>Is there another way to do this? Did I miss an obvious method from Commons Collections?</p> <h1>Related</h1> <p>I also spotted <a href="https://stackoverflow.com/questions/11758220/a-mechanism-for-having-different-equals-physical-equals-and-logical-equals-on">this question</a> on SO which is similar though in that case I'm thinking overriding <code>equals()</code> makes a little more sense.</p> <h2>Edit</h2> <p>Something very similar to this will be going into a release of <a href="http://commons.apache.org/proper/commons-collections/" rel="nofollow noreferrer">Apache Commons Collections</a> in the near future (at the time of this writing). See <a href="https://issues.apache.org/jira/browse/COLLECTIONS-446" rel="nofollow noreferrer">https://issues.apache.org/jira/browse/COLLECTIONS-446</a>.</p>
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    1. USMatt Lachman
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    1. COI think your approach is optimal. It pretty clean and easy.
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      1. USNikita Beloglazov
    2. COSince the answer with this comment was removed: I chose Comparator as opposed to some other interface because it is a well-known interface for custom Object comparison beyond `equals()` and `hashCode()`. A custom interface would work just as well but I didn't want to "reinvent the wheel."
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      1. USMatt Lachman
    3. CORelated: https://issues.apache.org/jira/browse/COLLECTIONS-242
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