constants

问题 I want to make a class to group some static const values. // SomeClass.dart class SomeClass { static const SOME_CONST = 'some value'; } What is the idiomatic way in dart to prevent dependent code from instantiating this class? I would also like to prevent extension to this class. In Java I would do the following: // SomeClass.java public final class SomeClass { private SomeClass () {} public static final String SOME_CONST = 'some value'; } So far all I can think of is throwing an Exception ,

问题 Is the any difference in performance and/or any other benefits we can get when using final keyword with constant utility class. [ This class contains only static final fields and private constructor to avoid object creation] public class ActionConstants { private ActionConstants() // Prevents instantiation { } public static final String VALIDFIRSTLASTNAME = "[A-Za-z0-9.\\s]+"; public static final String VALIDPHONENUMBER = "\\d{10}"; ... ... } Only diffrence is class is made final public final

问题 Is the any difference in performance and/or any other benefits we can get when using final keyword with constant utility class. [ This class contains only static final fields and private constructor to avoid object creation] public class ActionConstants { private ActionConstants() // Prevents instantiation { } public static final String VALIDFIRSTLASTNAME = "[A-Za-z0-9.\\s]+"; public static final String VALIDPHONENUMBER = "\\d{10}"; ... ... } Only diffrence is class is made final public final

问题 Example int main() { const int i = 1.0; // Notice I am assigning a double to an int here char a[i]; } Question Compiling the above code with g++ -O0 -Wall -pedantic -ansi -std=c++11 gives no errors (except for an unused variable). However, if I remove -std=c++11 , I get the following warning: warning: ISO C++ forbids variable length array According to this SO question, I believe that in C++03, the code is invalid. However, can someone explain how the rule has changed in C++11? (This question

问题 I have been looking about constants and I don't really understand whats different about them other than they cant be changed programmatically. extern NSString * const MyConstant; With this line what exactly does extern mean and what exactly does the const mean? 回答1: You're asked two questions here: one about constants and one about extern. The two aren't necessarily related. First, const : there isn't much more to constants than, as you said, they can't be changed programmatically. Different

问题 I have been looking about constants and I don't really understand whats different about them other than they cant be changed programmatically. extern NSString * const MyConstant; With this line what exactly does extern mean and what exactly does the const mean? 回答1: You're asked two questions here: one about constants and one about extern. The two aren't necessarily related. First, const : there isn't much more to constants than, as you said, they can't be changed programmatically. Different

问题 Can someone post an example of the shortest way of sharing a (preferably static final) string or number constant between Java code and UiBinder XML, where I can use the constant either in an attribute: <g:TextArea width="...px"/> or in a value: <g:Label>...</g:Label> I can't seem to find an example of this, only text from a file, which I don't want. 回答1: static fields (and enum constants) can be used with a simple <ui:import> : <ui:import field="com.example.Pojo.CONSTANT" /> or <ui:import

问题 Can someone post an example of the shortest way of sharing a (preferably static final) string or number constant between Java code and UiBinder XML, where I can use the constant either in an attribute: <g:TextArea width="...px"/> or in a value: <g:Label>...</g:Label> I can't seem to find an example of this, only text from a file, which I don't want. 回答1: static fields (and enum constants) can be used with a simple <ui:import> : <ui:import field="com.example.Pojo.CONSTANT" /> or <ui:import

问题 No matter which C-compatible library I use, when I look at the header defined constants, they are always defined as hexadecimal values. Here, for instance, in GL/gl.h: #define GL_POINTS 0x0000 #define GL_LINES 0x0001 #define GL_LINE_LOOP 0x0002 #define GL_LINE_STRIP 0x0003 #define GL_TRIANGLES 0x0004 #define GL_TRIANGLE_STRIP 0x0005 #define GL_TRIANGLE_FAN 0x0006 #define GL_QUADS 0x0007 #define GL_QUAD_STRIP 0x0008 #define GL_POLYGON 0x0009 Is there any particular reason for this convention,

问题 I am using a few Java classes like javax.Mail.Session and MessageDigest for a tool I am building. I noticed that it was difficult assigning them properties because they were using String constants for that. For example, for a Session object, you have to assign String key value pairs in a Property instance which is then used to create a Session . So if you want your session to log debugging messages, assign "smtp.mail.debug" , "true" in the Property instance. Similarly, if you want your