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    <p>Sorry to say, but @Jigar's answer is incorrect. This is the correct answer. (tldr; don't use <code>for : each</code>).</p> <pre><code>import java.util.ArrayList; import java.util.List; public class LoopTest { public static void main(String s[]) { long start, end; List&lt;Integer&gt; a = new ArrayList&lt;Integer&gt;(); for (int i = 0; i &lt; 2500000; i++) { a.add(i); } ///// TESTING FOR : EACH LOOP start = System.currentTimeMillis(); for (Integer j : a) { int x = j + 3; } end = System.currentTimeMillis(); System.out.println(end - start + " milli seconds for [ Integer j : a ] "); ////// TESTING DEFAULT LOOP start = System.currentTimeMillis(); for (int i = 0; i &lt; a.size(); i++) { int x = a.get(i) + 3; } end = System.currentTimeMillis(); System.out.println(end - start + " milli seconds for [ int i = 0; i &lt; a.length; i++ ] "); ////// TESTING SLIGHTLY OPTIMIZED LOOP start = System.currentTimeMillis(); int size = a.size(); for (int i = 0; i &lt; size; i++) { int x = a.get(i) + 3; } end = System.currentTimeMillis(); System.out.println(end - start + " milli seconds for [ int i = 0; i &lt; size; i++ ] "); //// TESTING MORE OPTIMIZED LOOP start = System.currentTimeMillis(); for (int i = size; --i &gt;= 0;) { int x = a.get(i) + 3; } end = System.currentTimeMillis(); System.out.println(end - start + " milli seconds for [ int i = size; --i &gt;= 0; ] "); } } </code></pre> <p>The results:</p> <pre><code>96 milli seconds for [ Integer j : a ] 57 milli seconds for [ int i = 0; i &lt; a.length; i++ ] 31 milli seconds for [ int i = 0; i &lt; size; i++ ] 31 milli seconds for [ int i = size; --i &gt;= 0; ] </code></pre> <p>You can make up your own mind, but too much attribution is given to the JVM optimizer. You still have to be smart with your own code, and using <code>for : each</code> notation is NOT a good idea (almost ever). As you can see, you have a good idea by putting size in its own variable.</p> <p>Even though some of these optimization may be JVM-dependent (and some may kick in with the JIT), it's important to know what Java does and what Java doesn't do.</p>
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    1. POfor loop optimization
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    1. USDavid Titarenco
    1. USDavid Titarenco
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    1. COu r right `for : each` is always been slow and call to frequent `.size()` is some what slow than assign to one varialble
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      1. USRavi Parekh
    2. COTry running your 'benchmark' with `LinkedList`.
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      1. USuser802421
    3. COSaying "that using for-each notation is NOT a good idea (almost ever)" is pretty silly. In the absolute majority of the cases, you are going to prefer readability over performance. In the few cases where your loop is a performance bottelneck, it might be worth it to investigate whether there is a more performant option.
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