The java.util.Properties class is meant to represent a map where the keys and values are both Strings. This is because Properties objects are used to read .properties files, which are text files. So, why in Java 5 did they retrofit this class to implement Map<Object,Object> and not Map<String,String>? The javadoc states: Because P...
I'm trying to build a generic grid view in an ASP.NET MVC application. Let me explain with some code: public interface ITrustGrid<T> { IPagedList<T> Elements { get; set; } IList<IColumn<T>> Columns { get; set; } IList<string> Headers { get; } } This is an interface of a class that allows me to set columns and expressions ...
Suppose I have the following class: public class FixExpr { Expr<FixExpr> in; } Now I want to introduce a generic argument, abstracting over the use of Expr: public class Fix<F> { F<Fix<F>> in; } But Eclipse doesn't like this: The type F is not generic; it cannot be parametrized with arguments <Fix<F>> Is this possible at ...
In an attempt to see if I can clean up some of my math code, mostly matrix stuff, I am trying to use some Java Generics. I have the following method: private <T> T[][] zeroMatrix(int row, int col) { T[][] retVal = (T[][])new Object[row][col]; for(int i = row; i < row; i++) { for(int j = col; j < col; j++) { r...
I've read Neal Gafter's blog on the subject and am still unclear on a number of points. Why is it not possible to create a implementations of the collections api that preserve type information given the current state of Java, the JVM and existing collections API? Couldn't these be them replace the existing implementations in a future ve...
Below is a question from Kathy & Bert Bates SCJP 5 preparation CD. I have posted this elsewhere too, but have not gotten a satisfactory explanation until now.... Please help me understand this: public class BackLister { //Insert code here { List<T> output=new LinkedList<T>(); for(T t:input) output.add(0,t); ...
I have implemented a sort of Repository class and it has has GetByID, DeleteByID methods and so on, but I'm having trouble implementing the UpdateByID method. I did something like this: public virtual void UpdateByID(int id, T entity) { var dbcontext = DB; var item = GetByID(dbcontext, id); item = entity; ...
I'm new to Java and very confused. I have a large dataset of length 4 int[] and I want to count the number of times that each particular combination of 4 integers occurs. This is very similar to counting word frequencies in a document. I want to create a Map<int[], double> that maps each int[] to a running count as the list is iterate...
I have an issue with a class that I'm trying to test. I've declared a private enum and I'm using that in a generic dictionary in the code. This enum has no meaning outside of this class but it's used in a private method. When I generated the code the accessor is written into the generic dictionary type, but throws an invalid cast exce...
I'm building a generic grid to use in ASP.NET MVC applications. I'm having troubles with making a partial view that gets a generic class passed to it. I have prepared a small sample project which demonstates what I want to do. Download it here. In the HomeController I have 2 controller actions that use my generic grid class to prepare ...
In the below code "where T : WsgTypes.RouteRestriction", can I add multiple classes so that T can be of only those few classes types which I am interested of public static T GetDetails<T>(string code) where T : WsgTypes.RouteRestriction { T details; if (typeof(T) == typeof(WsgTypes.TicketType)) { ...
This is more a question regarding generics than subsonic: Imagine if have the following code: List<int> result = DB.Select(Product.Columns.Id) .From<Product>() .ExecuteTypedList<int>(); That works great and returns a generic list with the ids from my Product table. But if I want to get a list of the Produc...
I have an array of Castle windsor registration components of type IRegistration[] In this case ComponentRegistration<T> : IRegistration For each element in my array, if it can be upcast to ComponentRegistration<> I would like to upcast it back to ComponentRegistration<T> and process it. How exactly would I do this? I got as far as ...
Pages have Roles. Users have Roles. A user may only view a page if he and it share one or more roles. This works: Dim Allow As Boolean = False CurrentPage.Roles.Load() For Each r As Role In CurrentPage.Roles r.Users.Load() For Each u As User In r.Users If u.Id = CurrentUser.Id Then Allow = True ...
First of all, let me apologize in case the title doesn't make sense. I'm having a hard time understanding what I'm doing, let alone being able to use the right words for describing what I'm doing. I'm building a generic grid class in which I define the columns by a header / linq expression combination: public class Column<T> { publ...
Consider this class: public class Column<T> { public string Header { get; set; } public Func<T, string> ValueExpression { get; set; } } used like this: var columns = new List<Column<Employee>> { new Column<Employee> {Header = "Employee Id", ValueExpression = e => e.EmployeeID.ToString()}, ...
I have a TreeSet, which will be full of integers. To make a long story short, I'm trying to loop starting after the last (greatest) value stored in the list. What I'm doing now to get the starting variable is: Object lastObj = primes.last(); Integer last = new Integer(lastObj.toString()); int start = 1 + last.intValue(); // ...
I have searched high and low for documentation on how to use this feature. While the loop I could write would be simple and take no time, I really would like to learn how to use this. Basically I have a class, say, Widget, with a Save() sub that returns nothing. So: Dim w as New Widget() w.Save() basically saves the widget. Now let'...
I am quite comfortable with generics and such, but in this special case I have a question concerning the "Type safety: Unchecked cast from .. to .." warning. Basically I have a List of Class objects and now I want to get a subset of these that implement a special interface but the resulting List should also have that special Type: ... ...
I'm writing a wrapper for the WinForms ComboBox control that will let me populate the dropdown with a List<T>, and has a Selected property that returns an item of type T (or null if nothing selected). Rather than having a Selected property, I'd like it to be named based on the generic type automatically. For example: MyDropDownList<Us...