Can anyone explain bit in detail about this rule. Rule:AccessorMethodGeneration Priority:3 Avoid autogenerated methods to access private fields and methods of inner / outer classes with concrete examples for both fields and methods?
The PMD documentation provides a summary of the AccessorMethodGeneration rule, with my emphasis added:
When accessing a private field / method from another class, the Java
compiler will generate a accessor methods with package-private
visibility. This adds overhead, and to the dex method count on
Android. This situation can be avoided by changing the visibility of
the field / method from private to package-private.
So PMD is advising you that if you make such members and methods package-private instead of private you will avoid the overhead of having to access them through compiler generated accessor methods. (I'm not an Android developer so I can't comment on the "dex method count" issue.)
This is the code example PMD provides with respect to private members:
public class OuterClass {
private int counter;
/* package */ int id;
public class InnerClass {
InnerClass() {
OuterClass.this.counter++; // wrong accessor method will be generated
}
public int getOuterClassId() {
return OuterClass.this.id; // id is package-private, no accessor method needed
}
}
}
And here is an SO example where the compiler will auto-generate code to access private methods. Note the poster's comment (with my emphasis added):
The compiler takes the inner classes and turns them into top-level
classes. Since private methods are only available to the inner class
the compiler has to add new "synthetic" methods that have package
level access so that the top-level classes have access to it.
In summary, PMD is flagging code where you can make performance improvements (which I would think would usually be very minor) in some scenarios by modifying the access on private members and private methods.
One other point worth noting is that there are some PMD bug reports on AccessorMethodGeneration not working properly (e.g. https://github.com/pmd/pmd/issues/274 and https://github.com/pmd/pmd/issues/342). So if you can't understand why PMD is flagging your code with a AccessorMethodGeneration warning, check the bug reports.
I have many classes (45 at least). Each one has its own method to validate something that is repeated in all the classes, so I have the code repeated in all those classes. I'd like to have one method and call it from all the classes.
If have the following code to know if a mobile device is connecting to the server
private boolean isMobileDevice(HttpServletRequest request) {
String userAgent = request.getHeader("user-agent");
return userAgent.indexOf("Windows CE") != -1;
}
As said before, This method is repeated in many classes
Is it possible in Intellij Idea and/or Eclipse to do that refactor? and How can I perform that refactor?
private boolean isMobileDevice(HttpServletRequest request) {
String userAgent = request.getHeader("user-agent");
return userAgent.indexOf("Windows CE") != -1;
}
I bet that my Eclipse will warn me that this method can be declared as static, because it does not use any fields of enclosing class - such method should be declared as static to let you know that it is not essentially needed in enclosing class, and if there will be a reason (having 45 methods in place of one is THE REASON) you can move it to some other class, and just call it as public or package method.
EDIT: It did: The method isMobileDevice(HttpServletRequest) from the type Test can be declared as static:
So:
Copy it to some other class, make it public static boolean isMobileDevice(HttpServletRequest request) and use in every classes where it was private boolean.
That's all, but I don't see and way to make it with automatic refactor.
With Intellij you could try "Refactor" > "Find and Replace Code Duplicates...".
It will replace the duplicate code by a static function.
I am using Xtext do define a new language. I wish to generate code from this language, however I do not want to use the automatically suggested doGenerate function. Instead, I need to use a java code (not Xtend), that I can call from the build process.
Of course in that java code I want to be able to use the 'resource' that is passed to the original suggested function, so I can access all the information from the DSL's code.
I Believe by default the generator is implementation is an xtend file but there is nothing stopping you from changing this to a java file, you just need to override the binding in your [LanguageName]RuntimeModule class as follows:-
public class ExampleRuntimeModule extends com.example.AbstractExampleRuntimeModule {
#Override
public Class<? extends IGenerator> bindIGenerator() {
return YourOwnGenerator.class;
}
}
Where YourOwnGenerator should implement IGenerator.
I'm in a generic method, debugging, but i get no information about variables, can't execute statements using ctrl-shift-i, eclipse tells the that the method ... isn't available on the type T.
I can't believe it's meant to (not) work like this ...
[edit]
I'm using the eclipse that's part of RAD 7.5.4
[another edit]
Here's some code but I doubt you'll get any info from this
public abstract class GenericGroupController<T extends Group> {
...
public String addUser(final Model model, final Long id, final WebRequest request) {
T group = groupManager.loadGroup(id);
...
// this method will fail if i highlight and click ctr-shift-i
// but it will work otherwise (actually so will the method above
// because that's generic as well)
Long groupId = group.getId();
...
return getAddUserView();
}
}
If you are able to debug, as in see a stack trace, you can always see the variables in the variables window if not in the code. A lot of places where the code isn't available you can do the same. It isn't nice, but, it gets the job done.
GWT.create() is the reflection equivalent in GWT,
But it take only class literals, not fully qualified String for the Class name.
How do i dynamically create classes with Strings using GWT.create()?
Its not possible according to many GWT forum posts but how is it being done in frameworks like Rocket-GWT (http://code.google.com/p/rocket-gwt/wiki/Ioc) and Gwittir (http://code.google.com/p/gwittir/wiki/Introspection)
It is possible, albeit tricky. Here are the gory details:
If you only think as GWT as a straight Java to JS, it would not work. However, if you consider Generators - Special classes with your GWT compiler Compiles and Executes during compilation, it is possible. Thus, you can generate java source while even compiling.
I had this need today - Our system deals with Dynamic resources off a Service, ending into a String and a need for a class. Here is the solutuion I've came up with - btw, it works under hosted, IE and Firefox.
Create a GWT Module declaring:
A source path
A Generator (which should be kept OUTSIDE the package of the GWT Module source path)
An interface replacement (it will inject the Generated class instead of the interface)
Inside that package, create a Marker interface (i call that Constructable). The Generator will lookup for that Marker
Create a base abstract class to hold that factory. I do this in order to ease on the generated source code
Declare that module inheriting on your Application.gwt.xml
Some notes:
Key to understanding is around the concept of generators;
In order to ease, the Abstract base class came in handy.
Also, understand that there is name mandling into the generated .js source and even the generated Java source
Remember the Generator outputs java files
GWT.create needs some reference to the .class file. Your generator output might do that, as long as it is referenced somehow from your application (check Application.gwt.xml inherits your module, which also replaces an interface with the generator your Application.gwt.xml declares)
Wrap the GWT.create call inside a factory method/singleton, and also under GWT.isClient()
It is a very good idea to also wrap your code-class-loading-calls around a GWT.runAsync, as it might need to trigger a module load. This is VERY important.
I hope to post the source code soon. Cross your fingers. :)
Brian,
The problem is GWT.create doen't know how to pick up the right implementation for your abstract class
I had the similar problem with the new GWT MVP coding style
( see GWT MVP documentation )
When I called:
ClientFactory clientFactory = GWT.create(ClientFactory.class);
I was getting the same error:
Deferred binding result type 'com.test.mywebapp.client.ClientFactory' should not be abstract
All I had to do was to go add the following lines to my MyWebapp.gwt.xml file:
<!-- Use ClientFactoryImpl by default -->
<replace-with class="com.test.mywebapp.client.ClientFactoryImpl">
<when-type-is class="com.test.mywebapp.client.ClientFactory"/>
</replace-with>
Then it works like a charm
I ran into this today and figured out a solution. The questioner is essentially wanting to write a method such as:
public <T extends MyInterface> T create(Class<T> clz) {
return (T)GWT.create(clz);
}
Here MyInterface is simply a marker interface to define the range of classes I want to be able to dynamically generate. If you try to code the above, you will get an error. The trick is to define an "instantiator" such as:
public interface Instantiator {
public <T extends MyInterface> T create(Class<T> clz);
}
Now define a GWT deferred binding generator that returns an instance of the above. In the generator, query the TypeOracle to get all types of MyInterface and generate implementations for them just as you would for any other type:
e.g:
public class InstantiatorGenerator extends Generator {
public String generate(...) {
TypeOracle typeOracle = context.getTypeOracle();
JClassType myTYpe= typeOracle.findType(MyInterface.class.getName());
JClassType[] types = typeOracle.getTypes();
List<JClassType> myInterfaceTypes = Collections.createArrayList();
// Collect all my interface types.
for (JClassType type : types) {
if (type.isInterface() != null && type.isAssignableTo(myType)
&& type.equals(myType) == false) {
myInterfaceTypes.add(type);
}
for (JClassType nestedType : type.getNestedTypes()) {
if (nestedType.isInterface() != null && nestedType.isAssignableTo(myType)
&& nestedType.equals(myTYpe) == false) {
myInterfaceTypes.add(nestedType);
}
}
}
for (JClassType jClassType : myInterfaceTypes) {
MyInterfaceGenerator generator = new MyInterfaceGenerator();
generator.generate(logger, context, jClassType.getQualifiedSourceName());
}
}
// Other instantiator generation code for if () else if () .. constructs as
// explained below.
}
The MyIntefaceGenerator class is just like any other deferred binding generator. Except you call it directly within the above generator instead of via GWT.create. Once the generation of all known sub-types of MyInterface is done (when generating sub-types of MyInterface in the generator, make sure to make the classname have a unique pattern, such as MyInterface.class.getName() + "_MySpecialImpl"), simply create the Instantiator by again iterating through all known subtypes of MyInterface and creating a bunch of
if (clz.getName().equals(MySpecialDerivativeOfMyInterface)) { return (T) new MySpecialDerivativeOfMyInterface_MySpecialImpl();}
style of code. Lastly throw an exception so you can return a value in all cases.
Now where you'd call GWT.create(clz); instead do the following:
private static final Instantiator instantiator = GWT.create(Instantiator.class);
...
return instantiator.create(clz);
Also note that in your GWT module xml, you'll only define a generator for Instantiator, not for MyInterface generators:
<generate-with class="package.rebind.InstantiatorGenerator">
<when-type-assignable class="package.impl.Instantiator" />
</generate-with>
Bingo!
What exactly is the question - i am guessing you wish to pass parameters in addition to the class literal to a generator.
As you probably already know the class literal passed to GWT.create() is mostly a selector so that GWT can pick and execute a generator which in the end spits out a class. The easist way to pass a parameter to the generator is to use annotations in an interface and pass the interface.class to GWT.create(). Note of course the interface/class must extend the class literal passed into GWT.create().
class Selector{
}
#Annotation("string parameter...")
class WithParameter extends Selector{}
Selector instance = GWT.create( WithParameter.class )
Everything is possible..although may be difficult or even useless. As Jan has mentioned you should use a generator to do that. Basically you can create your interface the generator code which takes that interface and compile at creation time and gives you back the instance. An example could be:
//A marker interface
public interface Instantiable {
}
//What you will put in GWT.create
public interface ReflectionService {
public Instantiable newInstance(String className);
}
//gwt.xml, basically when GWT.create finds reflectionservice, use reflection generator
<generate-with class="...ReflectionGenerator" >
<when-type-assignable class="...ReflectionService" />
</generate-with>
//In not a client package
public class ReflectionGenerator extends Generator{
...
}
//A class you may instantiate
public class foo implements Instantiable{
}
//And in this way
ReflectionService service = GWT.create(ReflectionService.class);
service.newInstance("foo");
All you need to know is how to do the generator. I may tell you that at the end what you do in the generator is to create Java code in this fashion:
if ("clase1".equals(className)) return new clase1();
else if ("clase2".equals(className)) return new clase2();
...
At the final I thought, common I can do that by hand in a kind of InstanceFactory...
Best Regards
I was able to do what I think you're trying to do which is load a class and bind it to an event dynamically; I used a Generator to dynamically link the class to the event. I don't recommend it but here's an example if it helps:
http://francisshanahan.com/index.php/2010/a-simple-gwt-generator-example/
Not having looked through the code of rocket/gwittir (which you ought to do if you want to find out how they did it, it is opensource after all), i can only guess that they employ deferred binding in such a way that during compile time, they work out all calls to reflection, and statically generate all the code required to implement those call. So during run-time, you cant do different ones.
What you're trying to do is not possible in GWT.
While GWT does a good job of emulating Java at compile time the runtime is of course completely different. Most reflection is unsupported and it is not possible to generate or dynamically load classes at runtime.
I had a brief look into code for Gwittir and I think they are doing their "reflection stuff" at compile time. Here: http://code.google.com/p/gwittir/source/browse/trunk/gwittir-core/src/main/java/com/totsp/gwittir/rebind/beans/IntrospectorGenerator.java
You might be able to avoid the whole issue by doing it on the server side. Say with a service
witch takes String and returns some sort of a serializable super type.
On the server side you can do
return (MySerializableType)Class.forName("className").newInstance();
Depending on your circumstances it might not be a big performance bottleneck.