Develop Reference

How can I generate and compile Java files in Android at Runtime

I know with javax.tools.* it is possible, but since this is not included in the Android API, I'm desperately wondering, is this possible?
Right now, my goal is to create a drag-and-drop tool to allow users to create their own layouts (as not everyone wants to learn Mobile Development, as it requires a lot of time, dedication and practice) similar to how Android Studio does it's own. However, of course the most important thing is to implement functionality via onClickListener and onTouchListeners. I've begun remedying this by creating my own DSL (Domain-Specific-Language) with a GUI front-end allowing users to choose what they want via PopupMenu and SubMenus. For example...
Statements
{ if, for, while }
Statements must be followed immediately by a reference and then a conditional (obtained from that reference), like a "if(Object.conditional())" statement.
References
{ Object1, Object2, Object3 }
The objects are references to other Views (I.E, Buttons, Layouts, WebView, etc.).
Conditionals|Actions|Getters|Setters
{ isSomething(), doSomething(), getSomething(), setSomething() }
Each Reference's methods, wrapped so that each wrapper keeps track of it's method's attributes and description (hence documentation).
It would go something like such...
IF ImageView1.isVisible()
ImageView1.setVisible(false)
ELSE
ImageView1.setVisible(true)
Of course, the method setVisible(boolean) is a wrapped version of setVisiblity(int).None of this is typed, it is obtained from a simple PopupMenu which shows them the applicable selections based on current context.
How I plan on transcribing this to compiling code was to convert the statement into Java code, inserting references on the fly as they are needed (I.E, ImageView1 would be defined in java as private ImageView ImageView1;), generate methods somewhat similar to how ButterKnife generates it's extra classes for it's onClick and onTouch annotations, etc.
Then, after planning all of this (been working on it for 2 weeks now), I find out that Android does not have support for compiling code like this. Please tell me something like this is possible. It's something I 100% wanted to do. Is this possible with any third party libraries?
If not, is there some possible way to mimic doing so? I could do it the long and slow way, of preparing every such possible way, keeping track of the references myself through a map, and when it is about to be called, directly call the implemented method for the View associated with that key, which theoretically COULD work. In fact, that'd be my second go-to if I can't. It'd be messy though.
Sorry if this is too long, I just want to get this to work.
TL;DR: Is there a way to compile a generated Java file created at Runtime in Android (since javax.tools.* does not exist), and if not what would be the best way to do so?

How to get a list of instances which are referencing another instance in Java? [duplicate]

Is there a way to see all the references to an object in execution time?
I'm using Netbeans, does this feature exist in it?
EDIT: No problem in using profilers to do this, I only need know the references, no matters how.

Ok, Netbeans show all the references to an object.
First, run the project in debug mode CTRL + F5, after, show the Loaded Classes Alt + Shift + 4 or Window->Debug->Loaded Classes.
Choose the class will want to see the references and double click on it.
Pause the execution and there is.
In the top is the attributes of the object, and in the bottom, all references to it.

If you dump the heap and analyse it, you find all references. Profilers like VisualVM and YourKit can do this for you.
However, it is not possible to determine this dynamically. If you want to know all the things which refer to an object, you must maintain a collection of them yourself.

In Netbeans you can use the Find Usages feature to see where a particular class may have been referenced inside of a particular project.
From the Project Explorer, select the class and right click > Find Usages.
The results looks a bit like the following image:

Sorry, was not clear. I want the references in the execution time. All
the refereces of a created object
Unfortunately, there is no such feature available in Java. But, there is a way of being notified that there is no more reference to an object at runtime.
The solution is to create a weak reference to the monitored object and associate it with a reference queue. When there will be no more hard reference to that object, the GC will sooner or later recollect it and enqueue the weak reference. You can check this with isEnqueued().
If you provide more information about your issue, may be we can give more tips & tricks.
EDIT
To control all references to an oject, you may use the Proxy Pattern. Instead of setting references to your connection object, you create a proxy object containing a private instance of the connection object. Then, have your code call the proxy who will call the connection object itself, instead of having direct references to the connection.
When you are done with the connection object, close it inside the proxy object. If other parts of the code still try to access that connection objects via the proxy, you will be able to detect it in the proxy when it is called.
It is a trick you can use to find which part of the code is still 'referencing' your object, so to speak.
Hope this helps.

Can java access global events created using CreateEvent

I am trying to access a global event created by native code in my java client. I am using JNA for this purpose to call OpenEvent method of kernel32.dll. But the method always returns NULL and GetLastError returns 2, which is File not found.
So I was wondering if JVM can see these global events and if so is there any other approach I can use?
--
Vinzy

How do you call your openEvent?
I suppose it's something like this
int result = kernel32.OpenEvent( 10000, false, "Global\\nameOfEvent" ); //request for deletion
with the only difference you may be using objects as arguments, which, I suppose, is a matter of preference.
Maybe if you provide the code for the call we might be able to help you. Another thing to be asked is if you call CreateEvent in your native code somewhere. If you dig into the Windows API, you will notice that:
"The function succeeds only if some
process has already created the event
by using the CreateEvent function."
source : http://msdn.microsoft.com/en-us/library/ms684305(v=vs.85).aspx
Which in your situation mean you will be in a lot trouble if you were not the one creating the event. There is a way of obtaining a handle to an event you did not create but it's a bit more complicated and let's start by you providing a bit more information.
Cheers.
To sum it up:
If you don't call CreateEvent anywhere in your code you will have trouble when calling OpenEvent. To escape this problem you would basically have to find which process/thread holds the lock to the event and make it give it to your thread (the jvm's).
If you do call CreateEvent in your code then you should not have any problems obtaining a reference to your event and the culprit is somewhere else.
In any case, a bit more code would be nice.

Possible to specify access to isAttribute vs getAttribute in JSP EL?

Our Topic object has BOTH isChannel and getChannel public methods. The object graph is too complex to change this. Channel has an Integer type.
We are migrating from one application server to Tomcat. When using this expression ${topic.channel.type}, in JSPs our current app server finds the getChannel method. However, Tomcat finds the isChannel method and we get errors since the return type is a Boolean, not a Channel. Is there a way to tell Tomcat to prefer getters over boolean public methods?
For now I'm just going to write a helper function or expose a new method, but I have a feeling I'm going to come across this quite a bit during the migration.

Unfortunately, you can't force a method call like that.
I have checked the Javabeans and EL specifications, but nowhere is specified what the preferred method is when both isXXX() and getXXX() methods are present. However, I do agree that it makes more sense to prefer the getXXX() one in this particular case. This should also be programmatically possible. I think it's worth the effort to report this as an issue against the Tomcat EL implementation.

In theory, this should be more of a JavaBeans issue than an EL implementation issue. One thing you might try is to find out how the java.beans.Introspector views your Topic class. One way to do that would be to run this code I wrote a while back for the Struts wiki. Depending on the complexity of your class, it might make sense to create an explicit java.beans.BeanInfo class to force the channel property to always be exposed as an Integer.

In Java, how can I construct a "proxy wrapper" around an object which invokes a method upon changing a property?

I'm looking for something similar to the Proxy pattern or the Dynamic Proxy Classes, only that I don't want to intercept method calls before they are invoked on the real object, but rather I'd like to intercept properties that are being changed. I'd like the proxy to be able to represent multiple objects with different sets of properties. Something like the Proxy class in Action Script 3 would be fine.
Here's what I want to achieve in general:
I have a thread running with an object that manages a list of values (numbers, strings, objects) which were handed over by other threads in the program, so the class can take care of creating regular persistent snapshots on disk for the purpose of checkpointing the application. This persistor object manages a "dirty" flag that signifies whether the list of values has changed since the last checkpoint and needs to lock the list while it's busy writing it to disk.
The persistor and the other components identify a particular item via a common name, so that when recovering from a crash, the other components can first check if the persistor has their latest copy saved and continue working where they left off.
During normal operation, in order to work with the objects they handed over to the persistor, I want them to receive a reference to a proxy object that looks as if it were the original one, but whenever they change some value on it, the persistor notices and acts accordingly, for example by marking the item or the list as dirty before actually setting the real value.
Edit: Alternatively, are there generic setters (like in PHP 5) in Java, that is, a method that gets called if a property doesn't exist? Or is there a type of object that I can add properties to at runtime?

If with "properties" you mean JavaBean properties, i.e. represented bay a getter and/or a setter method, then you can use a dynamic proxy to intercept the set method.
If you mean instance variables, then no can do - not on the Java level. Perhaps something could be done by manipulations on the byte code level though.
Actually, the easiest way to do it is probably by using AspectJ and defining a set() pointcut (which will intercept the field access on the byte code level).

The design pattern you are looking for is: Differential Execution. I do believe.
How does differential execution work?
Is a question I answered that deals with this.
However, may I suggest that you use a callback instead? You will have to read about this, but the general idea is that you can implement interfaces (often called listeners) that active upon "something interesting" happening. Such as having a data structure be changed.
Obligitory links:
Wiki Differential execution
Wiki Callback
Alright, here is the answer as I see it. Differential Execution is O(N) time. This is really reasonable, but if that doesn't work for ya Callbacks will. Callbacks basically work by passing a method by parameter to your class that is changing the array. This method will take the value changed and the location of the item, pass it back by parameter to the "storage class" and change the value approipriately. So, yes, you have to back each change with a method call.
I realize now this is not what you want. What it appears that you want is a way that you can supply some kind of listener on each variable in an array that would be called when that item is changed. The listener would then change the corresponding array in your "backup" to refect this change.
Natively I can't think of a way to do this. You can, of course, create your own listeners and events, using an interface. This is basically the same idea as the callbacks, though nicer to look at.
Then there is reflection... Java has reflection, and I am positive you can write something using it to do this. However, reflection is notoriously slow. Not to mention a pain to code (in my opinion).
Hope that helps...

I don't want to intercept method calls before they are invoked on the real object, but
rather I'd like to intercept properties that are being changed
So in fact, the objects you want to monitor are no convenient beans but a resurgence of C structs. The only way that comes to my mind to do that is with the Field Access call in JVMTI.

I wanted to do the same thing myself. My solution was to use dynamic proxy wrappers using Javassist. I would generate a class that implements the same interface as the class of my target object, wrap my proxy class around original class, and delegate all method calls on proxy to the original, except setters which would also fire the PropertyChangeEvent.
Anyway I posted the full explanation and the code on my blog here:
http://clockwork-fig.blogspot.com/2010/11/javabean-property-change-listener-with.html