Can a method present in the RequestContext method return void?
If my RequestContext looks like this,
#Service( value = PersonUtil.class, locator = PersonLocator.class )
public interface PersonRequest extends RequestContext
{
Request<void> testMethod( Long id );
......
}
I am getting this error:
Multiple markers at this line
- Return type for the method is missing
- Syntax error on token "void", Dimensions expected after
Can we not create a method with return type void? If not, why is it so?
Thanks in advance.
void is just like primitive types like int or boolean, you can't use it as a type parameter.
And just like you'd use Integer instead of int, you'll use Void here (java.lang.Void)
Related
I have an abstract base class validator with a method which takes a generic type as parameter.
I will be passing generic type parameter to base class from the subclass inheriting the base class.
Base Class:
abstract class BaseValidator {
bool isValid<T>(T obj);
}
Child Class:
class IPv4Validator extends BaseValidator{
final IPV4_REGEX = "^((25[0-5]|(2[0-4]|1d|[1-9]|)d).?\b){4}\$";
#override
bool isValid<String>(String obj) {
bool hasMatch = RegExp(IPV4_REGEX).hasMatch(obj);
return hasMatch;
}
}
Here hasMatch takes in non nullable string. When I directly pass some string hasMatch doesn't throw an error.
But when I try to pass the generic value in the method parameter, it shows an error.
The argument type 'String' can't be assigned to the parameter type
'String'.
I couldn't able to understand why generic type is not accepting, even though its compile-time type.
The following code solves this particular problem. But it may be different from what you intended to implement. On the other hand, the code will be cleaner if you create a new concrete class for different data types.
abstract class BaseValidator<T> {
bool isValid(T obj);
}
class IPv4Validator extends BaseValidator<String>{
final IPV4_REGEX = "^((25[0-5]|(2[0-4]|1d|[1-9]|)d).?\b){4}\$";
#override
bool isValid(String obj) {
bool hasMatch = RegExp(IPV4_REGEX).hasMatch(obj);
return hasMatch;
}
}
Explanation.
In the line class IPv4Validator extends BaseValidator<String> we are not declaring a new class BaseValidator, it is already declared as BaseValidator<T>. Here we are inheriting the specialization of the existing generic class BaseValidator. While in the line bool isValid<String>(String obj), we declare a new function, so the compiler understands it as if we were declaring a new generic function with a parameter type named String. So, here bool isValid<String>(String obj) is equivalent to bool isValid<T>(T obj), just instead of name T we used name String, which is not an object String.
another fix that you can do is to use the covariant keyword, to implement that, try this:
abstract class BaseValidator<T> {
bool isValid(T obj);
}
class IPv4Validator extends BaseValidator {
final IPV4_REGEX = "^((25[0-5]|(2[0-4]|1d|[1-9]|)d).?\b){4}\$";
#override
bool isValid(covariant String obj) {
bool hasMatch = RegExp(IPV4_REGEX).hasMatch(obj);
return hasMatch;
}
}
My question refers to Methods inside of Classes via "public" access.
As referring to mql4 documentation, there seems to be no listed source on how to properly instantiate a Method into a Class, or what even makes a Method a Method in the first place.
To me it seems that if you place a function inside of a Class, that in itself makes it a Method? Or am I wrong. Is anyone able to clear this up for me?
Basic information and differences between constructor and method:
Constructor:
A constructor is a special function, which is called automatically when creating an object of a structure or class and is usually used to initialize class members,
The name of a constructor must match the class name,
The constructor has no return type (you can specify the void type).
(docs)
Method:
A method is a function that belongs to a class or an object, i.e. it cannot exist without the class.
You need to declare class methods in the class. Else it wouldn't be a class method.
Method can return value with type specified in the method declaration.
Simple example:
class MyClass { // Declaration
private:
string myName; // Property
public:
void printName(); // Method of void return type
int sumIntegers(int a, int b); // Method of int return type
MyClass(string name); // Constructor declaration
};
MyClass::MyClass(string name) { // Constructor body
this.myName = name;
}
int MyClass::sumIntegers(int a, int b) { //Method body
return a + b;
}
void MyClass::printName() {
Print("Your name is: ", this.myName);
}
int sumIntegers(int a, int b){ //Function body
return a + b;
}
Class member (object) initialization:
MyClass *myObject = new MyClass("SO example");
Example usage inside OnInit:
int OnInit() {
myObject.printName(); // Method call by object (MyClass)
Alert("2 + 2 = ", myObject.sumIntegers(2, 2)); // Same as above
Alert("2 + 2 = ", sumIntegers(2, 2)); // Function call
return(INIT_SUCCEEDED);
}
To me it seems that if you place a function inside of a Class, that in
itself makes it a Method?
Yes, but remember that a function is a block of code which only runs when it is called, and it's not related with a class.
Methods are related with class, and can not exists without a class.
As the subject suggests, how does one enforce function argument types in editor (say VSCode) when the function itself is passed as an argument to a class constructor? This goes for complex types. In the simple example below, vscode linter doesn't hiccup when calling the passed add() function with incorrect (int) argument rather than the correct (String) argument:
class ChildClass {
final Function add;
ChildClass(this.add);
...
add('this is a string'); <---- HOW TO ENFORCE STRING ARGUMENT TYPE?
add(5); <----- EDITOR (VSCODE) should hiccup currently doesn't
}
class ParentClass {
int _add(String text) { <--- ARGUMENT OF TYPE STRING
// some code
}
final childClass = ChildClass(_add); <-- pass add() as argument to ChildClass ctor
}
Not sure if this is a vscode linter question or a dart question or both. Thoughts much appreciated.
You can specify function types inline
class ChildClass {
final int Function(String text) add;
or as typedef
typedef AddFn = int Function(string text);
class ChildClass {
final AddFn add;
See also
https://github.com/dart-lang/sdk/blob/master/docs/language/informal/generic-function-type-alias.md
https://www.dartlang.org/guides/language/language-tour#typedefs
given a block of Advice like below:
#Around("execution(* com.myproject..*(..))")
public Object log(ProceedingJoinPoint pjp) throws Throwable{
....
Object result = pjp.proceed();
......
return result;
}
I just want to know if I have a method that returns void, will this Advice get applied, and will that result in some kind of error?
Example:
package com.myproject.mypackage;
public Class MyClass {
public void run() {
// Will this method run properly as a result of 'pjp.proceed()' above?
}
}
Tried experimenting by running a few stub methods myself, I found that the Advice will get applied, and there will be no error other than those generated by the joinpoint itself.
public class A{
private void javaMethod(int a,int b){}
private native void init()/*-{
function OnMouseMove(e) {
//blow calling doesn't work
this.#p::javaMethod(Ljava/...teger;Ljava.../Integer;)(intVal,intVal);
}
}-*/;
}
As described above,how to make that invoking work?
Answered on the Google Group: https://groups.google.com/d/msg/google-web-toolkit/qE2-L4u_t4s/YqjOu-bUfsAJ
Copied here for reference and convenience:
First, int is not java.lang.Integer, so your method signature in JSNI is wrong; it should read javaMethod(II).
(I suppose the #p:: while javaMethod is defined in class A is over-simplification in your question, but is OK in your code)
You'll also probably have a problem with this, that might not be what you think it is. A common pattern is to assign the current object (this, at the time) to a variable that you'll reference from your closure:
var that = this;
…
function OnMouseMove(e) {
that.#p.A::javaMethod(II)(intVal, intVal);
}
You're doing two things wrong:
You're not defining the class name after #p, (assuming #p is actually just a shortened version of the real package's name);
You're attempting to pass java.lang.Integer in place of int. You should be saying (II) as the types, as described here.
Your code should look more like this:
package com.my.package;
public class ClassA {
private static void javaMethod(int a, int b) { ... }
public static native void init() /*-{
$wnd.javaMethod = function(a, b) {
return #com.my.package.ClassA::javaMethod(II)(a,b);
}
function OnMouseMove(e) {
$wnd.javaMethod(a,b);
}
}-*/;
}