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    <p>Long answer: <a href="http://burtleburtle.net/bob/hash/evahash.html#funneling" rel="nofollow">here</a></p> <p>Short answer: <br/>A <strong>funnel</strong> occurs when 2+ keys get hashed to the same value because of an error with the underlying hashing function. Like this:</p> <pre><code>Map&lt;String,Object&gt; myMap = new HashMap&lt;String,Object&gt;(); Thing thing1, thing2; thing1 = new Thing(); thing2 = new Thing(); myMap.put("ab", thing1); myMap.put("ba", thing2); </code></pre> <p>If there is an inherent flaw in the hashing function used by <code>HashMap&lt;K,V&gt;</code>, a "funnel" could occur where the keys <code>ab</code> and <code>ba</code> both map to, say, <code>thing1</code>.</p> <p>Think of a funnel as an actual funnel: multiple inputs get <em>funneled</em> into the same place.</p> <p><strong>Edit</strong><br/> If a hash function is flawed and does contain funnels, then a way to minimize their occurrence is to set the size of the table to being a prime number.</p> <p>This is because, in terms of being a "class" (category) of numbers, prime numbers have the least amount of factors. According to that article, funnels occur when a given key is a factor or multiple of the size of the table. So if we set the table size to 100 (not a prime number), we introduce the <em>possibility</em> of funneling when the provided key is any <em>factor of 100</em>: 1, 2, 4, 5, 10, ..., 100, 200, 300, etc.</p> <p>But if we make the size of the table to a prime, say, 101... then the only <em>possibility</em> of a funnel occurs at: 1, 101, 202, 302, etc. We've greatly reduced the <em>possibility</em> of a funnel.</p>
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    1. COi liked the first part of your answer....but link is too complex to understand....can you explain it...
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    2. COPlease see my edit explaining primes. Also the article is (probably) graduate level, and I'm just mere JEE developer with a bachelors degree! My original explanation of what a funnel is and how it occurs should be enough to give you the general idea though. Good luck!
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    3. COWhat is the difference between a funnel and a collision? Aren't collisions inevitable in hashing systems (but can be made improbable).
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