generics

问题 Below is the code, import java.util.List; import java.util.ArrayList; public class Dummy { public static void main(String[] args) { List<String> lst = new ArrayList<String>(); lst.add("a string"); lst.add("another string"); String s = lst.get(0); } //end main } when the constructor new ArrayList<String>(); is invoked, array of type Object is created. .. lst holds Object[0] array. So, If array of type Object gets created by constructor, How does javac does not see type casting issue in this

问题 I have a spec that requires me to pass an array of lists. The array is always length 2. I am using the following to accomplish this: List<MyClass> [] data = new ArrayList[2]; data[0] = new ArrayList<MyClass>(); data[1] = new ArrayList<MyClass>(); compiles but gives warning: uses unchecked or unsafe operations. I understand that Arrays of generics are not allowed in Java however I cannot change the spec and the above code seems to work nicely. As long as I am conscious that I never reassign

问题 I meet a problem today. As following. I create a generic Form , public class Form1:Form Then I create another inheritance form, public class From2:Form1. The form2 cannot be shown in the VS designer, the error message is "all the classes in the file cannot be designed", (this error message is translated from Chinese, the Chinese message is 文件中的类都不能进行设计). But this program can be compiled successfully, and when it runs, both Form1 and From2 can work. Anyone can give me some help about this ?

问题 I have a generic trait SomeTrait defined as so: trait SomeTrait[T] { def foo(t: T): String } And methods bar and qux as so: def bar[T](t: SomeTrait[T]): T def qux: List[SomeTrait[_]] I do not have control over the above. I am trying to operate on the list returned by qux , like so qux map { x => x.foo(bar(x))} However, the compiler complains that the types don't match up. As far as I know this should be fine. I have tried adding a generic method (signature [T](SomeTrait[T])String ), and

问题 Ts there any way to call a static member on type when I only have a generic parameter. For example if I have something like this public Get<T>(int id) { // I would like to do this string s = T.SomeMethodName(); } I could do it like this but is kinda "yucky", and then it does not matter if it is static or not. Or I could use reflection as suggested by Yuriy. ISomeKnownInterface i = (ISomeKnownInterface ) new T(); string s = i.SomeMethodName(); So question is now which is better approach,

问题 Ts there any way to call a static member on type when I only have a generic parameter. For example if I have something like this public Get<T>(int id) { // I would like to do this string s = T.SomeMethodName(); } I could do it like this but is kinda "yucky", and then it does not matter if it is static or not. Or I could use reflection as suggested by Yuriy. ISomeKnownInterface i = (ISomeKnownInterface ) new T(); string s = i.SomeMethodName(); So question is now which is better approach,

问题 I've created my own custom pseudo enumerations within my domain model to allow me to have some more verbose values. For example, my class is as follows: public abstract class Enumeration<X, Y> : IComparable where X : IComparable { public Enumeration(X value, Y displayName) { } public Y DisplayName { get { return _displayName; } } public X Value { get { return _value; } } } And a class that inherits it would be: public class JobType : Enumeration<string, string> { public static JobType

问题 I've created my own custom pseudo enumerations within my domain model to allow me to have some more verbose values. For example, my class is as follows: public abstract class Enumeration<X, Y> : IComparable where X : IComparable { public Enumeration(X value, Y displayName) { } public Y DisplayName { get { return _displayName; } } public X Value { get { return _value; } } } And a class that inherits it would be: public class JobType : Enumeration<string, string> { public static JobType

问题 I've created my own custom pseudo enumerations within my domain model to allow me to have some more verbose values. For example, my class is as follows: public abstract class Enumeration<X, Y> : IComparable where X : IComparable { public Enumeration(X value, Y displayName) { } public Y DisplayName { get { return _displayName; } } public X Value { get { return _value; } } } And a class that inherits it would be: public class JobType : Enumeration<string, string> { public static JobType

问题 I've created my own custom pseudo enumerations within my domain model to allow me to have some more verbose values. For example, my class is as follows: public abstract class Enumeration<X, Y> : IComparable where X : IComparable { public Enumeration(X value, Y displayName) { } public Y DisplayName { get { return _displayName; } } public X Value { get { return _value; } } } And a class that inherits it would be: public class JobType : Enumeration<string, string> { public static JobType