casting

问题 Let's say I have a Base class Employee and an derived class Manager , like below: class Employee { public: string Name; }; class Manager : public Employee { public: string Designation; }; While implementing some function like below: Employee* SomeFunction(bool SomeCondition) { Employee *Emp = NULL; if (SomeCondition) { //Code goes here : Both Implementation 1 and 2 work fine! } return Emp; } When SomeCondition is true, I want to return a non-null object of type Manager . In such a scenario,

问题 Lets say I have a page object [FindsBy(How = How.Id, Using = "buttonSignIn")] public IWebElement BtnSignin { get; set; } I am trying to pass that into this method to convert the IWebElement into a By element. public void MoveAndClick(IWebElement element) { var findElement = driver.FindElement((By)element); Actions act = new Actions(driver); act.MoveToElement(findElement); act.Click(findElement); act.Perform(); } I know that this piece of code will work without casting the element into a By

问题 I want to create a BarChart using MPAndroidChart but I get the following error java.lang.ClassCastException: com.github.mikephil.charting.data.Entry cannot be cast to com.github.mikephil.charting.data.BarEntry I first get the data from a different activity and use that. First activity: ArrayList<BarEntry> temperature = new ArrayList<>(); for (int i = 0; i < temp.length(); i++) { float temp_data = Float.parseFloat(temp.getJSONObject(i).getString("value")); float humid_data = Float.parseFloat

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Java Generics: Array containing generics I have a Java class which contains 2 methods which add and remove an element from an array. To make it generic it takes a subtype so it should be able to work on different types of objects. The problem is that when I instantiate it using MapEntry (where MapEntry is an implementation of java.util.Map.Entry) as the subtype. This results in a ClassCastException being thrown

问题 I have a very simple macro for which I want to typecast its output to int only. How to do that? #define Numbits(A) (sizeof(A)*CHAR_BIT) I tried: #define int Numbits(A)({int val; val = sizeof(A)*CHAR_BIT; return val;}) but it also doesn't work 回答1: Are you saying that #define Numbits(A) (int)(sizeof(A)*CHAR_BIT) didn't work? 来源： https://stackoverflow.com/questions/31443484/how-to-typecast-preprocessor-macros-to-output-int

问题 I keep getting this error when compiling my program. This is just a small part of my code, so if needed I will provide the rest of the code. Any ideas on why this is occuring? void strip_quotes(char s[]) { if (s[0]=='"') s=s+1; if (s[strlen(s)-2]=='"') s[strlen(s)-2]=NULL; } 回答1: As Dave has already correctly pointed out the reason for the compiler error: s[strlen(s)-2]=NULL; /* = (void*)0 */ There is another bug in the code that won't cause a compiler error: if (s[0]=='"') s=s+1; the

问题 The Java tutorial on type erasure doesn't seem to detail the specific rules of cast insertion by the compiler. Can someone please explain the specific rules that cause the transformation detailed by the tutorial (reproduced below): public class Node<T> { public T data; public Node(T data) { this.data = data; } public void setData(T data) { System.out.println("Node.setData"); this.data = data; } } public class MyNode extends Node<Integer> { public MyNode(Integer data) { super(data); } public

问题 why the cast is not working here? http://services.odata.org/Northwind/Northwind.svc/Orders?$filter=startswith(cast(OrderID, 'Edm.String'),'1') it says: No coercion operator is defined between types 'System.Int32' and 'System.String'. 回答1: OData doesn't support conversion to and from string. It supports conversions between related entity types and between numeric primitive types only. See http://msdn.microsoft.com/en-us/library/dd541472(v=PROT.10).aspx and the castExpression paragraph. It's

问题 I am trying to understand how decorator pattern works and how much I can "stretch" it to me needs. Following this example, I have extended classes XYZ. There exist derived classes "KLM" (from XYZ) Specifically, even though I have a decorator pattern, the derived decorator classes "KLM" have some functionality that does not show up in any of their base classes "XYZ", "D", "I" or "A". So while normally I would instantiate an object as I * inKLM = new L( new M( new K( new A ))); This would not

问题 I'm trying to retrieve some data from Firebase using addChildEventListener() like this (code is in a Service ): aReference.child(requestID).addChildEventListener(new ChildEventListener() { @Override public void onChildAdded(DataSnapshot dataSnapshot, String s) { if (dataSnapshot.getValue() != null) { // error on the line below Map<String, String> nUser = (Map<String, String>) dataSnapshot.getValue(); userNameAU = nUser.get("uName"); Log.d("uName", userNameAU); } ... ... }); but I'm getting