casting

问题 I am trying to accomplish a way to cast a given object that is derived from an interface to a different type that is also derived from the same interface. This to prevent having to completely rebuild the object. interface IItem { } class FryingPan : IItem { } class CookingPan : IItem { } But here is the catch, I don't 'know' what type I am casting to. I only know by a type variable. This is set from a combobox. Type SelectedItem { get; set; } Can this be done ( preferably without having to

问题 I have a generic class Position<E> and a concrete class Card . How do I create an array of type Position<Card> ? I tried: Position<Card>[] suitPositions = (Position<Card>[]) new Object[5]; but I get a ClassCastException. But when I try: Position<String>[] suitPositions = (Position<String>[]) new Object[5]; it works just fine. 回答1: Use the raw type to create the array: Position<String>[] suitPositions = new Position[5]; 来源： https://stackoverflow.com/questions/35821682/creating-an-array-of

问题 We've to implement an encryption for an external interface. The owner of the interface has given documentation of how to preform the same encryption on our side. However, this documentation is in C# and we work in PHP. Most of the parts we understand except for where they seem to typecast a hash to an int. Their code reads: // hashString exists and is a md5 a like string int[] keyBuffer = new int[hashString.length]; for (int i=0; i<hashString.length; i++) { keyBuffer[i] = (int)hashString[i];

问题 class A{ int a=10; public void show(){ System.out.println("Show A: "+a); } } class B extends A{ public int b=20; public void show(){ System.out.println("Show B: "+b); } } public class DynamicMethodDispatch { public static void main(String[] args) { A aObj = new A(); aObj.show(); //output - 10 B bObj = new B(); bObj.show(); //output - 20 aObj = bObj; //assigning the B obj to A.. aObj.show(); //output - 20 aObj = new B(); aObj.show(); //output - 20 System.out.println(bObj.b); //output - 20 /

问题 Hi everyone i had a issue with a code in C# .NET, I'm using a DLL for connect to OPC Servers the DLL that was used in a VB.NET project and works with no problem at all. I'm trying to show a list of available Servers in a ListBox, the code used in VB.NET (and works) is this one: Dim AllOPCServers As Object AllOPCServers = AnOPCServer.GetOPCServers ' Load the list returned into the List box for user selection Dim i As Short For i = LBound(AllOPCServers) To UBound(AllOPCServers)

问题 I tried to compile the following code: public static void main(String[] args){ for (char c = 'a'; c <='z'; c = c + 1) { System.out.println(c); } } When I try to compile, it throws: Error:(5, 41) java: incompatible types: possible lossy conversion from int to char The thing is, it does work if I write c = (char)(c + 1) , c += 1 or c++ . I checked and the compiler throws a similar error when I try char c = Character.MAX_VALUE + 1; but I see no way that the value of 'c' can pass 'char' type

问题 This question already has answers here : Array to Object and Object to Array in PHP - interesting behaviour (2 answers) Closed 6 years ago . I am casting an object to array and after that I am unable to access the resulting array by a key. This is the code print_r($new); $new = (array)$new; echo $new['EPPContactemail']; foreach($new as $attr=>$value) { echo "$attr => $value \n"; } And the output is EPPContact Object ( [id:EPPContact:private] => 6553377C74FC9899 [roid:EPPContact:private] =>

问题 following code behaves strange (at least for me): int testValue = 1234; this.ConversionTest( testValue ); private void ConversionTest( object value ) { long val_1 = (long) (int) value; // works long val_2 = (long) value; // InvalidCastException } I don't understand why the direct (explicit) cast to long doesn't work. Can someone explain this behaviour? Thanks 回答1: The value parameter of your ConversionTest method is typed as object ; this means that any value types -- for example, int --

问题 I stumbled across this code. std::ostringstream str; /// (some usage) assert( ! str ); What does ostringstream signify when used in a bool context? Is this possibly an incorrect usage that happens to compile and run? 回答1: It tells you if the stream is currently valid. This is something that all streams can do. A file stream, for example, can be invalid if the file was not opened properly. As a side note, this functionality (testing a stream as a bool) is achieved by overloading explicit

问题 Not really an issue (although it is conflicting with an if() statement we have), but when you type in strtotime('cast'), it returns an actual value that defaults to today's date. I was just wondering if anyone knew what significance the word cast has when it comes to time functions Thanks! 回答1: It maps to the timezone offset for "Australia/Adelaide". Example: echo date('Y-m-d H:i:s'), "\n", date('Y-m-d H:i:s', strtotime("cast")), "\n", date('Y-m-d H:i:s', strtotime("Australia/Adelaide"));