Both ConcurrentHashMap and Hashtable are Collection classes for storing key value pairs and they both provide fast element search with a supplied key. They have much in common. However, we will not discuss the similarities between them here, instead we will focus on the differences between them.ConcurrentHashMap and Hashtable are both thread safe. But the mechanism for thread safe is different between them. Hashtable is synchronized, it utilizes the synchronization mechanism; while ConcurrentHashMap uses segmentation to lock the data, it uses concurrent locks operations for thread safety inste...

Did you know that inserting 2^16 = 65536 specially crafted values into a normal PHP array can take 30 seconds? Normally this would take only 0.01 seconds.This is the code to reproduce it:<?php echo '<pre>';$size = pow(2, 16); // 16 is just an example, could also be 15 or 17$startTime = microtime(true);$array = array();for ($key = 0, $maxKey = ($size - 1) * $size; $key <= $maxKey; $key += $size) { $array[$key] = 0;}$endTime = microtime(true);echo 'Inserting ', $size, ' evil elements took ', $endTime - $startTime, ' seconds', "\n";$startTime = microtime(true);$array = arra...

IntroductionHash tables are a permutation of associative arrays (i.e. name => value pairs). If you use PHP, then you are very familiar with this type of data structure already since all PHP arrays are associative.The Javascript language implements very loose and somewhat limited support for associative arrays. Any JavaScript array can use other objects as keys, making it a hash, but there exists no formal constructor for initializing them and it is more or less unweildy to work with. A short example of a hash in JavaScript would be as follows:var myArray = new Array();myArray['one'] = 1;myA...