casting

问题 I have a collection of Points, with a LINEID and an ID_SEQ . The LINEID determines the unique Line-IDS, while the ID_SEQ determines the order of the points in a Line-ID. I want to transform Points to Lines, ordered by ID_SEQ and grouped by LINEID . With the package sp , I am able to achieve the desired results, but I want to do it with the sf package. What am I missing here? Here is some dummy data, the desired result illustrated with sp -functions and two attempts to do the same with sf ,

问题 I have a collection of Points, with a LINEID and an ID_SEQ . The LINEID determines the unique Line-IDS, while the ID_SEQ determines the order of the points in a Line-ID. I want to transform Points to Lines, ordered by ID_SEQ and grouped by LINEID . With the package sp , I am able to achieve the desired results, but I want to do it with the sf package. What am I missing here? Here is some dummy data, the desired result illustrated with sp -functions and two attempts to do the same with sf ,

问题 I am retrieving the center of a map view and i need to pass the longs and lats as doubles to my server for testing against the database . How would i go about converting mapView.getMapCenter().getLongitudeE6() to a double ? 回答1: Calling mapView.getMapCenter() returns a GeoPoint . GeoPoint.getLongitudeE6() and GeoPoint.getLatitudeE6() both return microdegrees (basically degrees * 1E6). So, in Java, to convert microdegrees to degrees simply do: public static double microDegreesToDegrees(int

问题 I am retrieving the center of a map view and i need to pass the longs and lats as doubles to my server for testing against the database . How would i go about converting mapView.getMapCenter().getLongitudeE6() to a double ? 回答1: Calling mapView.getMapCenter() returns a GeoPoint . GeoPoint.getLongitudeE6() and GeoPoint.getLatitudeE6() both return microdegrees (basically degrees * 1E6). So, in Java, to convert microdegrees to degrees simply do: public static double microDegreesToDegrees(int

问题 This question already has answers here : The performance impact of using instanceof in Java (24 answers) Closed 5 years ago . I have a colleague here in my project, who is deeply against the use of instanceof operator, because it "generates a lot of overhead", what is the reason for that? Is it true? Is there another way to check the type of the Object instead of using it? Because I find it very useful in some occasions. 回答1: It does generate some overhead, combined with the subsequent

问题 I'm trying to call a .NET method accepting a generic IEnumerable<T> from F# using a seq<U> such that U is a subclass of T. This doesn't work the way I expected it would: With the following simple printer: let printEm (os: seq<obj>) = for o in os do o.ToString() |> printfn "%s" These are the results I get: Seq.singleton "Hello World" |> printEm // error FS0001; //Expected seq<string> -> 'a but given seq<string> -> unit Seq.singleton "Hello World" :> seq<obj> |> printEm // error FS0193; //seq

问题 I have a question about interface and class implementing interface. This is my code: interface iMyInterface { public iMethod1(); } public class cMyClass implements iMyInterface { public iMethod1() { // some code } protected iMethod2() { // some code } } I would like to create an instance of iMyInterface as this : iMyInterface i = new cMyClass(); i.iMethod1(); It's ok, but how can I call iMethod2() from my interface instance? Is this working and safe: ((cMyClass)i).iMethod2(); Thanks for help.

问题 If I have a base class and two derived classes, and I want to implement the casting between the two derived classes by hand, is there any way to do that? (in C#) abstract class AbsBase { private int A; private int B; private int C; private int D; } class Imp_A : AbsBase { private List<int> E; } class Imp_B : AbsBase { private int lastE; } Generally I'll be casting from Imp_A -> Imp_B and I want the last value in the E list to be the 'LastE'. Also, what if there were three or more

问题 I have noticed that there are two ways to cast objects (the difference is the placement of the outer parenthesis): 1. SimpleType simpleType = ((SimpleType) (property.getType())); 2. SimpleType simpleType = ((SimpleType) property).getType(); Are they doing the same thing ? 回答1: Are they doing the same thing ? No they are not. The first one is casting your value returned from property.getType() to SimpleType . ( Invocation is done before Casting ) The second one is first casting your property

问题 I'm trying to convert a couple of binary strings back to int. However it doesn't convert all my binary strings, leaving me a java.lang.NumberFormatException exception. Here is my test code with 3 binary string: public class Bin { public static void main(String argvs[]) { String binaryString ; binaryString = Integer.toBinaryString(~0); //binaryString = Integer.toBinaryString(~1); //binaryString = "1010" ; int base = 2; int decimal = Integer.parseInt(binaryString, base); System.out.println(