order-of-execution | 易学教程

When does a java object become non-null during construction?

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问题 Say you are creating a java object like so: SomeClass someObject = null; someObject = new SomeClass(); At what point does the someObject become non-null? Is it before the SomeClass() constructor runs or after? To clarify a little, say if another thread was to check if someObject was null while the SomeClass() constructor was halfway through completion, would it be null or non-null? Also, what would be the difference if someObject was created like so: SomeClass someObject = new SomeClass();

Script is before /body but it runs before page is loaded

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问题 I am new to web developing and I am trying node.js with express. I have the following directory structure: First App ---- node_modules ---- public -------- scripts ------------ additems.js ---- views -------- home.ejs ---- app.js with bold is a folder and italic is a file. this is the file additem.js: console.log("js connected"); alert("test"); and this is home.ejs file: <!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial

Java with NetBeans 7.2.1 - Execution order issue

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问题 Consider the following two classes in a NetBeans Java application. The main class: public class ExcecutionOrder { public static void main(String[] args) { Worker worker = new Worker(); worker.init(); worker.doProcessing(); worker.stop(); } } And a worker class like this: public class Worker { public void init() { System.out.println("\n-------------------------------------------------"); System.out.println("Worker initialized."); System.out.println("--------------------------------------------

++ operator returns original value if placed after operand — how?

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问题 As far as I've been led to understand, x++ is essentially a terser way of saying x = x + 1 . So far, so clear. In front-end Javascript, I've occasionally seen ++x — I seem to remember from a jsPerf test I can no longer find (how does one Google ++ effectively?) that this somehow had a small performance benefit in a particular version of IE, and let it go at that. However I've recently encountered something that speaks of a weird quirk in execution order (JS code): var x = 1; console.log(x++);

r Regular expression for extracting UK postcode from an address is not ordered

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问题 I'm trying to extract UK postcodes from address strings in R, using the regular expression provided by the UK government here. Here is my function: address_to_postcode <- function(addresses) { # 1. Convert addresses to upper case addresses = toupper(addresses) # 2. Regular expression for UK postcodes: pcd_regex = "[Gg][Ii][Rr] 0[Aa]{2})|((([A-Za-z][0-9]{1,2})|(([A-Za-z][A-Ha-hJ-Yj-y][0-9]{1,2})|(([A-Za-z][0-9][A-Za-z])|([A-Za-z][A-Ha-hJ-Yj-y][0-9]?[A-Za-z])))) {0,1}[0-9][A-Za-z]{2})" # 3.

Does Java reordering affect System.currentTimeMillis()?

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问题 According to Java Memory Model, instructions can be reordered as long as the execution is well-formed. So I wonder, is it possible that the following codes produces the following output? [codes][in a same thread] long a = System.currentTimeMillis(); long b = System.currentTimeMillis(); long c = System.currentTimeMillis(); [output] a == 10, b == 20, c == 15 If not possible, then what does JVM / implementations do to prevent this from happening? 回答1: Please see this question Instruction

AngularJS directive - setting order for multiple directive elements (not priority for directives, but priority for the elements)

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问题 Considering this markup with a directive "foo": <div foo run="3"></div> <div foo run="1"></div> <div foo run="2"></div> What is a good approach for causing "foo" to run in the specified order rather than from top to bottom (3,1,2)? The only thing I can think to do would be tracking what has run and returning false on the items that are not in order, then making angular try to run them all again and repeat until they are all done. That sounds terrible to me though, because it would have to

Do external stylesheets get loaded before the HTML?

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问题 If I have external stylesheets being included in the <head></head> section of my HTML page, will they be loaded before the HTML and immediately applied upon rendering? Let me present my specific use case. External styles.css file: form label { display: none; } Page containing form: <head> <link rel="stylesheet" href="styles.css" type="text/css" /> </head> <form action="process.php" method="post"> <label for="name">Name</label> <input type="text" id="name" name="name" /> </form> Can I be

AngularJS directive - setting order for multiple directive elements (not priority for directives, but priority for the elements)

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Considering this markup with a directive "foo": <div foo run="3"></div> <div foo run="1"></div> <div foo run="2"></div> What is a good approach for causing "foo" to run in the specified order rather than from top to bottom (3,1,2)? The only thing I can think to do would be tracking what has run and returning false on the items that are not in order, then making angular try to run them all again and repeat until they are all done. That sounds terrible to me though, because it would have to repeat so many times... Does Angular have something built-in that can be used? Is there an ideal approach

Why do these snippets of JavaScript behave differently even though they both encounter an error?

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问题 var a = {} var b = {} try{ a.x.y = b.e = 1 // Uncaught TypeError: Cannot set property 'y' of undefined } catch(err) { console.error(err); } console.log(b.e) // 1 var a = {} var b = {} try { a.x.y.z = b.e = 1 // Uncaught TypeError: Cannot read property 'y' of undefined } catch(err) { console.error(err); } console.log(b.e) // undefined 回答1: Actually, if you read the error message properly, case 1 and case 2 throw different errors. Case a.x.y : Cannot set property 'y' of undefined Case a.x.y.z :