Tutorial by Examples: n

The following example code is slower than it needs to be : Map<String, String> map = new HashMap<>(); for (String key : map.keySet()) { String value = map.get(key); // Do something with key and value } That is because it requires a map lookup (the get() method) for each ...

The Java Collections Framework provides two related methods for all Collection objects: size() returns the number of entries in a Collection, and isEmpty() method returns true if (and only if) the Collection is empty. Both methods can be used to test for collection emptiness. For example: C...

MySQL does not support the FULL OUTER JOIN, but there are ways to emulate one. Setting up the data -- ---------------------------- -- Table structure for `owners` -- ---------------------------- DROP TABLE IF EXISTS `owners`; CREATE TABLE `owners` ( `owner_id` int(11) NOT NULL AUTO_INCREMENT,...

Let's say you have a library that returns callbacks, for example the fs module in NodeJS: const fs = require("fs"); fs.readFile("/foo.txt", (err, data) => { if(err) throw err; console.log(data); }); We want to convert it to a promise returning API, with bluebird - ...

You can convert a single function with a callback argument to a Promise-returning version with Promise.promisify, so this: const fs = require("fs"); fs.readFile("foo.txt", (err, data) => { if(err) throw err; console.log(data); }); becomes: const promisify = requ...

In order to convert any callback API to promises assuming the promisify and promisifyAll version doesn't fit - you can use the promise constructor. Creating promises generally means specifying when they settle - that means when they move to the fulfilled (completed) or rejected (errored) phase to i...

var firstItem = fetch("/api1").then(x => x.json()); var secondItem = fetch("/api2").then(x => x.json()); Promise.all([firstItem, secondItem]).spread((first, second) => { // access both results here, both requests completed at this point });

#include <stdio.h> #include <math.h> #include <omp.h> #define N 1000000 int main() { double sum = 0; double tbegin = omp_get_wtime(); #pragma omp parallel for reduction( +: sum ) for ( int i = 0; i < N; i++ ) { sum += cos( i ); } ...

program typical_loop use omp_lib implicit none integer, parameter :: N = 1000000, kd = kind( 1.d0 ) real( kind = kd ) :: sum, tbegin, wtime integer :: i sum = 0 tbegin = omp_get_wtime() !$omp parallel do reduction( +: sum ) do i = 1, N sum = ...

On a 8 cores Linux machine using GCC version 4.4, the C codes can be compiled and run the following way: $ gcc -std=c99 -O3 -fopenmp loop.c -o loopc -lm $ OMP_NUM_THREADS=1 ./loopc Computing 1000000 cosines and summing them with 1 threads took 0.095832s $ OMP_NUM_THREADS=2 ./loopc Computing 100...

Ω-notation is used for asymptotic lower bound. Formal definition Let f(n) and g(n) be two functions defined on the set of the positive real numbers. We write f(n) = Ω(g(n)) if there are positive constants c and n0 such that: 0 ≤ c g(n) ≤ f(n) for all n ≥ n0. Notes f(n) = Ω(g(n)) means that f(n)...

Let f(n) and g(n) be two functions defined on the set of the positive real numbers, c, c1, c2, n0 are positive real constants. Notationf(n) = O(g(n))f(n) = Ω(g(n))f(n) = Θ(g(n))f(n) = o(g(n))f(n) = ω(g(n))Formal definition∃ c > 0, ∃ n0 > 0 : ∀ n ≥ n0, 0 ≤ f(n) ≤ c g(n)∃ c > 0, ∃ n0 > 0 ...

The PHP community has a lot of developers creating lots of code. This means that one library’s PHP code may use the same class name as another library. When both libraries are used in the same namespace, they collide and cause trouble. Namespaces solve this problem. As described in the PHP referenc...

realloc is conceptually equivalent to malloc + memcpy + free on the other pointer. If the size of the space requested is zero, the behavior of realloc is implementation-defined. This is similar for all memory allocation functions that receive a size parameter of value 0. Such functions may in fact ...

Expression trees represent code in a tree-like data structure, where each node is an expression Expression Trees enables dynamic modification of executable code, the execution of LINQ queries in various databases, and the creation of dynamic queries. You can compile and run code represented by expr...

Several 'insert' functions can "burn" ids. Here is an example, using InnoDB (other Engines may work differently): CREATE TABLE Burn ( id SMALLINT UNSIGNED AUTO_INCREMENT NOT NULL, name VARCHAR(99) NOT NULL, PRIMARY KEY(id), UNIQUE(name) ) ENGINE=InnoDB; IN...

to check if the given path exists path = '/home/john/temp' os.path.exists(path) #this returns false if path doesn't exist or if the path is a broken symbolic link

to check if the given path is a directory dirname = '/home/john/python' os.path.isdir(dirname) to check if the given path is a file filename = dirname + 'main.py' os.path.isfile(filename) to check if the given path is symbolic link symlink = dirname + 'some_sym_link' os.path.islink(symli...

A class or struct can have member functions as well as member variables. These functions have syntax mostly similar to standalone functions, and can be defined either inside or outside the class definition; if defined outside the class definition, the function's name is prefixed with the class' nam...

A common use of member functions is for encapsulation, using an accessor (commonly known as a getter) and a mutator (commonly known as a setter) instead of accessing fields directly. class Encapsulator { int encapsulated; public: int get_encapsulated() const { return encapsulated; }...