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    <p>You should be aware of the fact that your original attempt </p> <pre>int count = map.containsKey(word) ? map.get(word) : 0;</pre> <p>contains two potentially expensive operations on a map, namely <code>containsKey</code> and <code>get</code>. The former performs an operation potentially pretty similar to the latter, so you're doing the same work <em>twice</em>!</p> <p>If you look at the API for Map, <code>get</code> operations usually return <code>null</code> when the map does not contain the requested element.</p> <p>Note that this will make a solution like</p> <pre>map.put( key, map.get(key) + 1 );</pre> <p>dangerous, since it might yield <code>NullPointerException</code>s. You should check for a <code>null</code> first. <p><p> <b>Also note</b>, and this is very important, that <code>HashMap</code>s <em>can</em> contain <code>nulls</code> by definition. So not every returned <code>null</code> says "there is no such element". In this respect, <code>containsKey</code> behaves <em>differently</em> from <code>get</code> in actually telling you <em>whether</em> there is such an element. Refer to the API for details. <p><p> For your case, however, you might not want to distinguish between a stored <code>null</code> and "noSuchElement". If you don't want to permit <code>null</code>s you might prefer a <code>Hashtable</code>. Using a wrapper library as was already proposed in other answers might be a better solution to manual treatment, depending on the complexity of your application.</p> <p>To complete the answer (and I forgot to put that in at first, thanks to the edit function!), the best way of doing it natively, is to <code>get</code> into a <code>final</code> variable, check for <code>null</code> and <code>put</code> it back in with a <code>1</code>. The variable should be <code>final</code> because it's immutable anyway. The compiler might not need this hint, but its clearer that way.</p> <pre> final HashMap map = generateRandomHashMap(); final Object key = fetchSomeKey(); final Integer i = map.get(key); if (i != null) { map.put(i + 1); } else { // do something } </pre> <p>If you do not want to rely on autoboxing, you should say something like <code>map.put(new Integer(1 + i.getValue()));</code> instead.</p>
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    1. POMost efficient way to increment a Map value in Java
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    1. USAleksandar Dimitrov
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    1. COTo avoid the problem of initial unmapped/null values in groovy I end up doing: counts.put(key, (counts.get(key) ?: 0) + 1) // overly complex version of ++
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      1. USJoe Atzberger
    2. COOr, most simply: counts = [:].withDefault{0} // ++ away
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