Browse questions answered by Jon Skeet

C# object instance not working properly

I have a class Node as below: public class Node { public Dictionary<string, string> dictionary; public Node(Dictionary<string, string> dictionary) { ...

because I didn't add an item with key "2" at this.dictionary. Yes you did. You did it with this call: tmp.AddE(tmp, "String2","2"); That adds an entry with key "2" and value "String2" to the dictionary referred to by tmp... which... more 7/3/2016 4:28:34 PM

Use of the executeUpdate(String) method is not supported on this type of statement

PreparedStatement pstmt; for (int i = 0; i < cnt; i++) { String squery = "insert into response(seat_no,question_no,ans_opt,screenshot) values(?,?,?,?)"; pstmt =...

You've already specified the SQL when you prepared the statement: pstmt = con.prepareStatement(squery); You shouldn't then use Statement.executeUpdate(String) - instead, just use the parameterless executeUpdate() method: int num =... more 7/3/2016 2:13:44 PM

one of the parameters of a binary operator must be the containing type c#

public static int[,] operator *(int[,] arr1, int[,] arr2) { int sum; int[,] res = new int[arr1.GetLength(0), arr2.GetLength(1)]; for (int i = 0; i <...

The compiler is already telling you what is wrong - but to quote section 7.3.2 of the C# 5 specification: User-defined operator declarations always require at least one of the parameters to be of the class or struct type that contains... more 7/2/2016 9:49:01 AM

Why is Regex.Match not matching the same strings as Regex.Matches?

I made a find and replace dialog with a regex option. There is a button to test a regex, highlighting all matches, and a button to find individual matches. With some regular...

I suspect you have a space or something at the start of the text selected by your RichTextBox. At that point, it makes total sense. Look at your regular expression: (duplicate of )*([0-9]:+)* That will match the empty string. So for... more 7/2/2016 7:14:28 AM

Automatically call base method prior the derived one

I have a base class: abstract class ClassPlugin { public ClassPlugin(eGuiType _guyType) { GuiType = _guyType; } public eGuiType GuiType; ...

The standard solution to this is to use the template method pattern: public abstract class Base { // Note: this is *not* virtual. public void SomeMethod() { // Do some work here SomeMethodImpl(); // Do... more 7/1/2016 8:28:34 AM

How to select the latest dateTime of every week ? C#

I have to implement an algorithm who receive a list of DateTime and its recovers the latest DateTime of every week. Example: 29/06/2016 -> Lastest date of the last week of...

Note: this answer assumes that you're interested in "natural" weeks, which don't really care about the year. For example, December 31st 2015 was a Thursday, and January 1st 2016 was a Friday - to my mind (and using the algorithm in this... more 7/1/2016 8:14:27 AM

How assign a method reference value to Runnable

I hava a problem about Java 8 Runnable. public static void main(String[] args) { Runnable r1 = Test::t1; Runnable r2 = Test::t2; Runnable r3 = Test::t3; } public...

r2 is fine due to section 15.13.2 of the JLS, which includes: A method reference expression is congruent with a function type if both of the following are true: The function type identifies a single compile-time declaration... more 6/30/2016 9:15:32 AM

Why is .NET `PixelFormat` has an `Format8bppIndexed` element?

A group of 8 bits can store 256 values. A gray level can have 256 variations. So, why do they need Format8bppIndexed? Why is it Indexed? Why not Format8bpp ?

It's indexed because each value is an index into a colour table, which may well be RGB or RGBA with considerably more depth. For example, you could have a palette of 32-bit entries (8 bits for each of red, green, blue and alpha), but the... more 6/29/2016 7:08:34 PM

Cast of parameterized delegate to non parameterized analogue

Can anyone suggest why I cannot cast non-generic delegate to generic with appropriate type parameters? Particularly having two delegates as shown below public delegate void...

Simply put, they're different types. Imagine you had two classes like this: public class A1 { public int Value { get; set; } } public class A2 { public int Value { get; set; } } They're different classes despite looking... more 6/29/2016 5:32:39 AM

TcpClient getting disposed automatically

Using using (NetworkStream stream = client.GetStream()) Causes the socket to close.

I believe this is the problem: using (NetworkStream stream = client.GetStream()) That is automatically closing the stream at the end of the block, which in turn (I believe) closes the socket. The documentation is frankly unclear on this... more 6/28/2016 4:09:39 PM