null

问题 And can I therefore safely refactor all instances of class Blah { // ... private $foo = null; // ... } to class Blah { // ... private $foo; // ... } ? 回答1: Simple answer, yes. See http://php.net/manual/en/language.types.null.php The special NULL value represents a variable with no value. NULL is the only possible value of type null. You can easily test by performing a var_dump() on the property and you will see both instances it will be NULL class Blah1 { private $foo; function test() { var

问题 And can I therefore safely refactor all instances of class Blah { // ... private $foo = null; // ... } to class Blah { // ... private $foo; // ... } ? 回答1: Simple answer, yes. See http://php.net/manual/en/language.types.null.php The special NULL value represents a variable with no value. NULL is the only possible value of type null. You can easily test by performing a var_dump() on the property and you will see both instances it will be NULL class Blah1 { private $foo; function test() { var

问题 In the Dynamic web application I facing some issues,so I'm posting my code: Here is my controller(servlet): String select = request.getParameter("select"); // getting proper value String search = request.getParameter("search"); // getting proper value request.setAttribute("select", select); request.setAttribute("search", search); System.out.println("Select : "+select+" Search : "+search); int page = 1; int recordsPerPage = 20; if(request.getParameter("page") != null) page = Integer.parseInt

问题 Being new to Windows Store app development, I am working on an app that has to connect to several USB devices. I am using VS 2013 (community) with C#. For example, a list of attached webcams is obtained using: var devices = await DeviceInformation.FindAllAsync(DeviceClass.VideoCapture); This indeed gives me a list of attached webcams. To access the first device, a UsbDevice object should be created using: DeviceInformation device = devices[0]; UsbDevice usbDevice = await UsbDevice.FromIdAsync

问题 I have this query in SQL Server 2005 (I used the more convenient 2008 insert method for example only) and I need the (null) to be replaced with 0 in the grid output. Anyway to do this? 回答1: You would use the ISNULL() function. See SQL Fiddle SELECT 'lessonid response ->' , isnull([0], 0) as [0] , isnull([1], 0) as [1] , isnull([2], 0) as [2] , isnull([3], 0) as [3] , isnull([4], 0) as [4] FROM ( SELECT lessonid AS 'lessonid response ->' ,ISNULL(response,0) as response ,count(response) AS

问题 hey guys: I've been building a website with some animated rollovers, where I animate the background image to give a colour fade effect. It works fine in FF3, Safari, chrome, but IE8 throws the "undefined is null or not an object" error. Full text: Message: 'undefined' is null or not an object Line: 22 Char: 16 Code: 0 URI: http://www.philipdukes.co.uk/jquery.bgpos.js Message: 'undefined' is null or not an object Line: 22 Char: 16 Code: 0 URI: http://www.philipdukes.co.uk/jquery.bgpos.js In my

问题 When my chrome extension loads on chrome startup, everything seems to be ok and chrome.extension.getBackgroundPage() returns the right value (lunched from popup.js). But after awhile (2-3 minutes), especially if the browser is let alone, the function returns null. Only closing and re-opening chrome solves the problem. I tried to manipulate it by: if (chrome.extension.getBackgroundPage() == null) window.location.reload(true); As suggested at Why does chrome.extension.getBackgroundPage() return

问题 as far as i understood the AVG() function ignores NULL Values. So AVG(4,4,4,4,4,NULL) --> 4 In my case i don´t want this to happen. I need a solution like that: AVG(4,4,4,4,4,NULL) --> 3,33 without replacing the NULL values directly in the table itself. Is there any way to do this? 回答1: Use coalesce() to return the real value of zero for null columns: select avg(coalesce(some_column, 0)) from ... 回答2: You are correct about the behavior of AVG - use COALESCE to convert the NULLs to 0 in the

问题 my question is return; the same as return NULL; in C++? I understand that in C++, return NULL; is the same as return 0; in the context of pointers. Obviously for integers, this is not the case as NULL cannot be added, subtracted, etc. And that it is encouraged by some to use 0 instead of NULL for pointers because it is more convenient for portability. I'm curious if this is another instance where an equivalence occurs. I suspect that they are equivalent because return; is saying return

问题 I'm developing a LALG compiler to my college course on Java 1.6. So I did a types class and grammar class. EnumTypes public enum EnumTypes { A("OLA"), B("MUNDO"), C("HELLO"), D("WORLD"), /** * The order below is reversed on purpose. * Revert it and will you get a NULL list of types furder. */ I(EnumGrammar.THREE), H(EnumGrammar.TWO), F(EnumGrammar.ONE), E(EnumGrammar.ZERO); private String strValue; private EnumGrammar enumGrammarValue; private EnumTypes(String strValue) { this.strValue =