generics

问题 In implementation of a generic stack ,the following idiom is used and works without any problem public class GenericStack<Item> { private int N; private Item[] data; public GenericStack(int sz) { super(); data = (Item[]) new Object[sz]; } ... } However when I try the following ,it causes a ClassCastException String[] stra = (String[]) new Object[4]; Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String; How do you explain this? 回答1:

问题 In implementation of a generic stack ,the following idiom is used and works without any problem public class GenericStack<Item> { private int N; private Item[] data; public GenericStack(int sz) { super(); data = (Item[]) new Object[sz]; } ... } However when I try the following ,it causes a ClassCastException String[] stra = (String[]) new Object[4]; Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String; How do you explain this? 回答1:

问题 Can someone explain to me what this code is doing, I am new to java. Queue <TreeNode> queue = new LinkedList<TreeNode>(); I believe this code creates a Queue with the variable name queue that is of type TreeNode , what does the right side mean? Is it assigning the Queue to be a Linked List of type TreeNode ? 回答1: Class java.util.Queue uses type parameters to assure that you won't add type other than it was created with. If you create Queue like: Queue <TreeNode> queue = new LinkedList

问题 Can someone explain to me what this code is doing, I am new to java. Queue <TreeNode> queue = new LinkedList<TreeNode>(); I believe this code creates a Queue with the variable name queue that is of type TreeNode , what does the right side mean? Is it assigning the Queue to be a Linked List of type TreeNode ? 回答1: Class java.util.Queue uses type parameters to assure that you won't add type other than it was created with. If you create Queue like: Queue <TreeNode> queue = new LinkedList

问题 This question already has answers here : Closed 9 years ago . Possible Duplicate: Java how to: Generic Array creation I want to create a Stack which contains 10 elements, I'm trying to do this with Generics. I started by creating a Stack class of Type T, but I'm getting compilation error when I try to instantiate the array of generic type. public class Stack<T>{ private T[] stk = new T[10]; } What I'm doing wrong here? 回答1: You can't do this. Not without using some hacky round about code, and

问题 This question already has answers here : Closed 9 years ago . Possible Duplicate: Java how to: Generic Array creation I want to create a Stack which contains 10 elements, I'm trying to do this with Generics. I started by creating a Stack class of Type T, but I'm getting compilation error when I try to instantiate the array of generic type. public class Stack<T>{ private T[] stk = new T[10]; } What I'm doing wrong here? 回答1: You can't do this. Not without using some hacky round about code, and

问题 I'm trying to create the type of an array of objects. The first and second key of this object is required to match. For example: [{ key1: "hi", key2: "world" },{ key1: 1, key2: 2 },{ key1: true, key2: false }] This is what I've come up with but it doesn't exactly work. I have a generic type to define the object in the array. When calling it to generate the array type, an error is raised. type ArrayItem<T> = { key1: T, key2: T } // This raises an error Generic Type ArrayItem requires 1 type

问题 I did a little experiment on generics in C# and I had a problem where I want to pass a generic type as a type parameter with a constraint to implement a generic interface whose type I don't know. Here is my example: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace ConsoleApplication3 { class Program { interface IGenericCollection<T> { IEnumerable<T> Items { get; set; } } abstract class GenericCollection<T> :

问题 Here's a test that should, in my opinion be passing but is not. [TestMethod] public void can_get_open_generic_interface_off_of_implementor() { typeof(OpenGenericWithOpenService<>).GetInterfaces().First() .ShouldEqual(typeof(IGenericService<>)); } public interface IGenericService<T> { } public class OpenGenericWithOpenService<T> : IGenericService<T> { } Why does this not pass? Given Type t = typeof(OpenGenericWithOpenService<>) how do I get typeof(IGenericService<>)? I'm generally curious, but

问题 I have the following method: public static IResult<T, String> Validate<T>(this T value) { } // Validate How can I restrict T to be Int16, Int32, Int64, Double and String? 回答1: You can't restrict generics in that way, you can only choose a single class as a constraint. You must either make 5 overloads or find a interface all 5 of those things share and use that. Which option you choose will depend on what Validate doe. Here is how you would do the overloads. public static IResult<Int16, String