Develop Reference

Find Method usages only for specified class in Intelij-Idea

I am using IntelliJ IDEA and I have problem with method usage finding.
Suppose I have interface Worker.
public interface Worker {
void startWork();
void endWork();
}
And I have two implementations.
public class Develper implements Worker {
#Override
public void startWork() {
System.out.println("Developer Start Working");
}
#Override
public void endWork() {
}
}
public class Qa implements Worker {
#Override
public void startWork() {
System.out.println("QA start Work");
}
#Override
public void endWork() {
}
}
I open the Developer class and trying to find usages of startWork().
I want only to view usage of the Developer.startWork() implemented method.
But when I find usages it shows both Developer and Qa.startWork() method usages. How can I avoid Qa.startWork() method usage when finding Developer.startWork() usages?

Using Ctrl+Shift+Alt+F7 (⌘+⇧+⌥+F7 for Mac) should show the prompt from Jim Hawkins answer.
See: https://www.jetbrains.com/help/idea/find-usages-method-options.html
When you search for usages of a method implementation with this dialog Ctrl+Shift+Alt+F7, IntelliJ IDEA will ask whether or not you want to search for the base method. With any other find usages actions such as Alt+F7 or Ctrl+Alt+F7, the base method will be included in the search results automatically.

I'm using IntelliJ IDEA 15.0.1 .
I think what you see when using the "find usages" functionality depends from the context.
If you place the cursor in method name Developer.startWork and invoke find usages , you should see a small dialog. You are asked "Do you want to find usages of the base method?" .
If you say "No", and in your sources you did only call the method via the base class or interface (Worker.start() in your example), IDEA doesn't show you any hits. Thats correct.
If you call the overridden method via Developer.startWork() , and press "No" in the dialog, then you will see the usages of the specific implementation.
Update:

After reading the answer from #JimHawkins, I think the elephant is still in the room :) The question is, do you want to see where Developer.startWork() is actually called, or do you want to see where it is statically referenced?
Eg:
Developer developer = new Developer();
developer.startWork(); // you want to find only this?
Worker worker = developer;
worker.startWork(); // ..or this as well?
The find usages method can only tell, where a given method is statically referenced, but not where it is actually used (that is determined runtime via the mechanism of polymorphism).

Detecting if a listener has been registered

How can I detect if a new listener has been registered for any widget in my android app? Is there a place where I can intercept the listener when it's being registered?

I may be misunderstanding but you could do something like:
public interface ListenerChangeListener { // Feel free to remove the redundancy :P
public void listenerAdded(ListenerChangeEvent e);
public void listenerRemoved(ListenerChangeEvent e);
}
And
public class ListenerChangeEvent extends AWTEvent // or other class {
// Implementation
}
Finally, subclass your own custom widgets and modify the addXListener() and removeXListener() methods to fire your custom events if any have been added to the component. Then you just create your "Listener" class as per normal and implement your new Listener interface and so on.
It's a bit long and drawn out, again, I may have misunderstood exactly what you were after.

You can get a list of listeners on an object through a getter method (e.g. getActionListeners () on AbstractButton), and check if the one you have added is in the list.

Why do I need to overide "onPlaceRequest" in every Presenter class?

I'm managing the History in my project via Places.
What I do is this:
implement PlaceRequestHandler on top level (for example AppController),
register it -> eventBus.addHandler(PlaceRequestEvent.getType(), this);
implement method "onPlaceRequest" ,where i do project navigation.
I'm using GWT presenter and every presenter in my project overrides the onPlaceRequest method.
Why do I need this, when every request is handled from the top level "onPlaceRequest" method?
I will give an example:
public class AppController implements Presenter, PlaceRequestHandler
...........
public void bind()
{
eventBus.addHandler(PlaceRequestEvent.getType(), this);
...
}
public void onPlaceRequest(PlaceRequestEvent event)
{
// here is the project navigation tree
}
and let's take one presenter
public class SomePresenter extends Presenter<SomePresenter.Display>
{
... here some methods are overriden and
#Override
protected void onPlaceRequest(PlaceRequest request)
{
// what should I do here?
}
}
What is the idea, and how I'm supposed to use it?

Instead of making all of your presenters extend PlaceRequestHandler and managing those events yourself, you can attach a PlaceHistoryHandler and a PlaceController to your event bus. Together, they manage the browser's history and your places for you. When you ask your PlaceController to goTo() a different place, it will stop your current activity and use a mapping of places to activities (your presenters) to choose which one to start next.
To use this technique, you need to have your presenters extend AbstractActivity. Try following through Google's tutorial about it in GWT's documentation called GWT Development with Activities and Places.

java MVC + vetoable/deferred property

I have an interface FooModel and a class DefaultFooModel that have a few simple properties. I am getting stuck on a boolean enable property because I want to have this be vetoable/deferred:
public interface FooModel {
public boolean isEnabled();
/** returns old value */
public boolean setEnable(boolean enable);
public void addFooListener(FooModel.Listener listener);
public void removeFooListener(FooModel.Listener listener);
public interface Listener {
public void onFooEnableUpdate(boolean newEnable, boolean oldEnable);
}
}
What I want is for the model M to be the central point of access for the enable property. But here's the sequence of events that I want to occur:
view V (or any user of the model M) calls FooModel.setEnable(enable) on an arbitrary thread.
FooModel may either:
a. immediately call onFooEnableUpdate(newEnable, oldEnable) on each of its listeners in arbitrary order
b. start a potentially long sequence of events whereby another entity (e.g. controller C) can decide whether to enable, and somehow let FooModel know, whereby the enable property may be updated and then we proceed as usual in (a) above.
The thing is, I'm not sure how to go about doing this.
Approach 1: the mechanism to do this shouldn't be part of the model's interface. Instead, my DefaultFooModel has an implementation which accepts a FooController:
public interface FooController {
public void onFooEnableRequest(boolean newEnable, boolean oldEnable);
}
When DefaultFooModel.setEnable() is called, it then calls FooController.onFooEnableRequest(). The controller is expected to return immediately, but can take its time to digest the request, and then later call DefaultFooModel.updateEnable() which causes the real onFooEnableUpdate() to get called.
Approach 2: build something into the FooModel interface, but I'm not sure what.
Approach 3: Don't build anything into FooModel, just have it handle a regular property. Instead have the Controller listen to FooModel.onFooEnableUpdate() and override setEnable right away to the old value, then call FooModel.setEnable() later to set the new value.
Any advice?

Make FooModel a class instead of an interface.
The problem I see with making FooModel an interface is the complex logic that needs to be coded into the listener mechanism. It's generally not a good idea to force anyone who implements the interface to have to implement the listener logic as well.
Instead, make FooModel a class, implement the listener interface yourself, and creatively create public methods that can be overridden where you need to implement more specific functionality.
notifyListeners(boolean newEnable, boolean oldEnable) notifies all listeners, by default by calling the following method, but could be overridden to do nothing, or to notify conditionally
notifyListener(Listener listener, boolean newEnable, boolean oldEnable) notifies a specific listener

Is there a recommended way to use the Observer pattern in MVP using GWT?

I am thinking about implementing a user interface according to the MVP pattern using GWT, but have doubts about how to proceed.
These are (some of) my goals:
the presenter knows nothing about the UI technology (i.e. uses nothing from com.google.*)
the view knows nothing about the presenter (not sure yet if I'd like it to be model-agnostic, yet)
the model knows nothing of the view or the presenter (...obviously)
I would place an interface between the view and the presenter and use the Observer pattern to decouple the two: the view generates events and the presenter gets notified.
What confuses me is that java.util.Observer and java.util.Observable are not supported in GWT. This suggests that what I'm doing is not the recommended way to do it, as far as GWT is concerned, which leads me to my questions: what is the recommended way to implement MVP using GWT, specifically with the above goals in mind? How would you do it?

Program Structure
This is how I did it. The Eventbus lets presenters (extending the abstract class Subscriber) subscribe to events belonging to different modules in my app. Each module corresponds to a component in my system, and each module has an event type, a presenter, a handler, a view and a model.
A presenter subscribing to all the events of type CONSOLE will receive all the events triggered from that module. For a more fine-grained approach you can always let presenters subscribe to specific events, such as NewLineAddedEvent or something like that, but for me I found that dealing with it on a module level was good enough.
If you want you could make the call to the presenter's rescue methods asynchronous, but so far I've found little need to do so myself. I suppose it depends on what your exact needs are. This is my EventBus:
public class EventBus implements EventHandler
{
private final static EventBus INSTANCE = new EventBus();
private HashMap<Module, ArrayList<Subscriber>> subscribers;
private EventBus()
{
subscribers = new HashMap<Module, ArrayList<Subscriber>>();
}
public static EventBus get() { return INSTANCE; }
public void fire(ScEvent event)
{
if (subscribers.containsKey(event.getKey()))
for (Subscriber s : subscribers.get(event.getKey()))
s.rescue(event);
}
public void subscribe(Subscriber subscriber, Module[] keys)
{
for (Module m : keys)
subscribe(subscriber, m);
}
public void subscribe(Subscriber subscriber, Module key)
{
if (subscribers.containsKey(key))
subscribers.get(key).add(subscriber);
else
{
ArrayList<Subscriber> subs = new ArrayList<Subscriber>();
subs.add(subscriber);
subscribers.put(key, subs);
}
}
public void unsubscribe(Subscriber subscriber, Module key)
{
if (subscribers.containsKey(key))
subscribers.get(key).remove(subscriber);
}
}
Handlers are attached to components, and are responsible for transforming native GWT events into events specialised for my system. The handler below deals with ClickEvents simply by wrapping them in a customised event and firing them on the EventBus for the subscribers to deal with. In some cases it makes sense for the handlers to perform extra checks before firing the event, or sometimes even before deciding weather or not to send the event. The action in the handler is given when the handler is added to the graphical component.
public class AppHandler extends ScHandler
{
public AppHandler(Action action) { super(action); }
#Override
public void onClick(ClickEvent event)
{
EventBus.get().fire(new AppEvent(action));
}
Action is an enumeration expressing possible ways of data manipulation in my system. Each event is initialised with an Action. The action is used by presenters to determine how to update their view. An event with the action ADD might make a presenter add a new button to a menu, or a new row to a grid.
public enum Action
{
ADD,
REMOVE,
OPEN,
CLOSE,
SAVE,
DISPLAY,
UPDATE
}
The event that's get fired by the handler looks a bit like this. Notice how the event defines an interface for it's consumers, which will assure that you don't forget to implement the correct rescue methods.
public class AppEvent extends ScEvent {
public interface AppEventConsumer
{
void rescue(AppEvent e);
}
private static final Module KEY = Module.APP;
private Action action;
public AppEvent(Action action) { this.action = action; }
The presenter subscribes to events belonging to diffrent modules, and then rescues them when they're fired. I also let each presenter define an interface for it's view, which means that the presenter won't ever have to know anything about the actual graphcal components.
public class AppPresenter extends Subscriber implements AppEventConsumer,
ConsoleEventConsumer
{
public interface Display
{
public void openDrawer(String text);
public void closeDrawer();
}
private Display display;
public AppPresenter(Display display)
{
this.display = display;
EventBus.get().subscribe(this, new Module[]{Module.APP, Module.CONSOLE});
}
#Override
public void rescue(ScEvent e)
{
if (e instanceof AppEvent)
rescue((AppEvent) e);
else if (e instanceof ConsoleEvent)
rescue((ConsoleEvent) e);
}
}
Each view is given an instance of a HandlerFactory that is responsible for creating the correct type of handler for each view. Each factory is instantiated with a Module, that it uses to create handlers of the correct type.
public ScHandler create(Action action)
{
switch (module)
{
case CONSOLE :
return new ConsoleHandler(action);
The view is now free to add handlers of different kind to it's components without having to know about the exact implementation details. In this example, all the view needs to know is that the addButton button should be linked to some behaviour corresponding to the action ADD. What this behaviour is will be decided by the presenters that catch the event.
public class AppView implements Display
public AppView(HandlerFactory factory)
{
ToolStripButton addButton = new ToolStripButton();
addButton.addClickHandler(factory.create(Action.ADD));
/* More interfacy stuff */
}
public void openDrawer(String text) { /*Some implementation*/ }
public void closeDrawer() { /*Some implementation*/ }
Example
Consider a simplified Eclipse where you have a class hierarchy to the left, a text area for code on the right, and a menu bar on top. These three would be three different views with three different presenters and therefore they'd make up three different modules. Now, it's entirely possible that the text area will need to change in accordance to changes in the class hierarchy, and therefore it makes sense for the text area presenter to subscribe not only to events being fired from within the text area, but also to events being fired from the class hierarchy. I can imagine something like this (for each module there will be a set of classes - one handler, one event type, one presenter, one model and one view):
public enum Module
{
MENU,
TEXT_AREA,
CLASS_HIERARCHY
}
Now consider we want our views to update properly upon deletion of a class file from the hierarchy view. This should result in the following changes to the gui:
The class file should be removed from the class hierarchy
If the class file is opened, and therefore visible in the text area, it should be closed.
Two presenters, the one controlling the tree view and the one controlling the text view, would both subscribe to events fired from the CLASS_HIERARCHY module. If the action of the event is REMOVE, both preseneters could take the appropriate action, as described above. The presenter controlling the hierarchy would presumably also send a message to the server, making sure that the deleted file was actually deleted. This set-up allows modules to react to events in other modules simply by listening to events fired from the event bus. There is very little coupling going on, and swapping out views, presenters or handlers is completely painless.

I achieved something on these lines for our project. I wanted a event-driven mechanism (think of PropertyChangeSupport and PropertyChangeListener of standard jdk lib) which were missing. I believe there is an extension module and decided to go ahead with my own. You can google it for propertychangesupport gwt and use it or go with my approach.
My approach involved logic centred around MessageHandler and GWTEvent. These serve the same purpose as that of PropertyChangeListener and PropertyChangeEvent respectively. I had to customize them for reasons explained later. My design involved a MessageExchange, MessageSender and MessageListener. The exchange acts as a broadcast service dispatching all events to all listeners. Each sender fires events that are listened by the Exchange and the exchange the fires the events again. Each listener listens to the exchange and can decide for themselves (to process or not to process) based on the event.
Unfortunately MessageHandlers in GWT suffer from a problem: "While a event is being consumed, no new handlers can be hooked". Reason given in the GWT form: The backing iterator holding the handlers cannot be concurrently modified by another thread. I had to rewrite custom implementation of the GWT classes. That is the basic idea.
I would've posted the code, but I am on my way to airport right now, will try to post the code as soon as I can make time.
Edit1:
Not yet able to get the actual code, got hold of some power-point slides I was working on for design documentation and created a blog entry.
Posting a link to my blog article: GXT-GWT App
Edit2:
Finally some code soup.
Posting 1
Posting 2
Posting 3

have a look at: http://www.gwtproject.org/javadoc/latest/com/google/gwt/event/shared/EventBus.html
(which outdates http://www.gwtproject.org/javadoc/latest/com/google/web/bindery/event/shared/EventBus.html)
It should run fine with GWT as I'll try right now myself.