these lines appears in the generated file of .jj file
ASTSQLSchemaStatement jjtn000 = new ASTSQLSchemaStatement(JJTSQLSCHEMASTATEMENT);
boolean jjtc000 = true;
jjtree.openNodeScope(jjtn000);
Together they create a new node and open its scope. (And declare a boolean var.) The node's scope will remain open until it is closed or abandoned. While it is open, it may acquire children. When it is closed it will be pushed on a stack and may become the child of some other open node. See https://javacc.java.net/doc/JJTree.html for more details.
ASTSQLSchemaStatement jjtn000 = new ASTSQLSchemaStatement(JJTSQLSCHEMASTATEMENT);
This will create an instance of an object of type ASTSQLSchemaStatement.
boolean jjtc000 = true;
This will create a primitive boolean with the value true.
jjtree.openNodeScope(jjtn000);
This is a method call on a variable called jjtree (I don't know what type this is), sending the instance of ASTSQLSchemaStatement we created earlier.
Related
How do I make it so the TreeView is populated with ProgressIndicators while stuff is happening, but without blocking the thread, using a cell factory?
How does TreeItem.setGraphic() differ from TreeCell.setGraphic()?
When I instantiate the TreeItem, I need to set the graphic to a ProgressIndicator, but I'm not sure whether this ought to happen while creating the TreeItem or from the TreeCell.updateItem dumped out by the factory.
I think when using cell factories, all graphical stuff needs to happen there, thus TreeItem.setGraphic is merely a convenience, and I should figure out my problem from within updateItem.
I'm doing the file explorer example. Each item in the TreeView has the value set to a sun.nio.fs.WindowsPath, and is implemented by inheriting from TreeItem. I override isLeaf() and getChildren(). The problem is isLeaf() can take a long time on network drives when I'm not plugged into the network.
So this is what I'm doing to create a new tree item with a path value (not using cell factory yet):
Start new thread (using Clojure futures) to check if the path value is a path or file using isRegularFile(). The result from this is available later when dereferencing the future.
Instantiate instance of anonymous TreeItem derivative (using Clojure proxy).
Call setGraphic() on the new TreeItem instance with a ProgressIndicator().
Start another thread which checks the result of the first thread. When the first thread is finished, then based on the value of the leaf function, the first thread sets the appropriate file or folder icon, and calls addEventHandler() with local anonymous functions that change the graphic based on expanded or collapsed.
Return the new instance of TreeItem (from step 2) before either of the new threads is finished.
This works and has the effect of putting a swirly graphic at each network drive while isLeaf is running. But I'm not sure how to do all this when both TreeItem and TreeCell seem to have a setGraphic() function; I'm not sure who "owns" what. I think the TreeView owns the both the items and the cells, and calling setGraphic() on a TreeItem somehow references the default cell's graphic, when not using a custom cell factory.
I need to figure out how to access the isLeaf value from the cell factory updateItem(), etc. etc.
I need to continue writing to the same file using a file output stream, However I'm implementing the program using a javafx GUI from different windows. but:
Since you can not access a global variable without intializing the stream as final I have to make it final however,
Since I have to wrap the the Stream in a try catch, the variable is not recognised as initialised.
I was previously intialising in method like this
eW = outputFactory .createXMLEventWriter(new FileOutputStream("File.txt"));
However, that obivously overwrites the same file when you write the same statement again.
So essentially my question is, how can you set a final variable that needs to be surrounded in a try catch?
final File file = new File("File.txt");
final FileOutputStream fileOS = new FileOutputStream(file);
You don't need to initialize a variable as final to access it from different threads or objects. There are other ways to do it.
You can use a helper class, or even a helper thread. The second option is better in (the most common) case where you have more than 1 thread in your project. You can then use a normal try-catch block that has a (almost infinite) while loop inside, that checks a write queue and writes something when needed.
If you only use 1 thread and only append to a file, you may want to do just that - open the file to append, rather than overwrite. There's a boolean flag in the constructor.
You can take a look at the FileOutputStream(File file, boolean append) constructor, which would allow you to append to the end of the file rather than overwrite each time.
I do not know how you implemented it, but if you are writing to the same file from multiple windows, it might be easier to have a helper class which exclusively handles writing to file. This would allow you to centralize your File output code to one place making it easier to debug and maintain.
I have a specification of a function that acts like a constructor. The specification of the function is
function Create_Controller return Type_Controller;
Also, in the specification file, I have the Type_Controller type, which is an access. I copy the relevant fragment:
type Type_Controller_Implementation;
type Type_Controller is access Type_Controller_Implementation;
So, this is what I've attempted:
function Create_Controller return Type_Controller
is
My_Controller : aliased Type_Controller_Implementation;
begin
return My_Controller'Access;
end Create_Controller;
I tried to compile the program without the aliased keyword, but then, the compiler says:
prefix of "Access" attribute must be aliased
So, I put the aliased keyword and the compiler now suggests that I should change the specification:
result must be general access type
add "all" to type "Controlador_De_Impresion" defined at controller.ads
The problem is that I'm not allowed to change the specification. I've read the chapter about access types in the Ada Programming Wikibook, but I still don't understand why my code doesn't work. What am I doing wrong?
The implementation of the Create_Controller function body is incorrect. Were it to work as coded, you'd be returning a pointer to a variable local to that function body's scope...which would be immediately lost upon returning from the function, leaving you with an invalid pointer.
No, an instance of the type needs to be allocated and returned. If there's no explicit initialization that needs to occur you can simply do:
return new Type_Controller_Implementation;
If there is some initialization/construction that has to occur, then:
function Create_Controller return Type_Controller
is
My_Controller : Type_Controller := new Type_Controller_Implementation;
begin
-- Set fields of My_Controller
...
return My_Controller;
end Create_Controller;
When you declare an access type as access T, you're saying that "this is a pointer to a T and it must point to objects of type T allocated from a pool". (That is, allocated with a new keyword.) When you declare an access type as access all T, you're saying that it can point either to a T allocated from a pool, or to an aliased variable of type T.
If the type is declared as access T and you can't change it, then all access values of the type have to point to something allocated with new. You can't make it point to a variable (even to a "global" variable that isn't located on the stack).
The reasons for this are historical, I think. The first version of Ada (Ada 83) only had "pool-specific types." You couldn't make an access value point to some other variable at all, without trickery. This meant that a compiler could implement access values as indexes into some storage block, or as some other value, instead of making them the actual address of an object. This could save space (an access value could be smaller than an address) or allow more flexibility in how pool memory was managed. Allowing access values to point directly to objects takes away some of that flexibility. I think that's why they decided to keep the old meaning, for backward compatibility, and require an all keyword to indicate the new kind of access.
My Flex app uses local SharedObjects. There have been incidents of the Flash cookie getting corrupt, for example, due to a plugin crash. In this case SharedObjects.getLocal will throw an exception (#2006).
My client wants the app to recover gracefully: if the cookie is corrupt, I should replace it with an empty one.
The problem is, if SharedObject.getLocal doesn't return an instance of SharedObject, I've nothing to call clear() on.
How can I delete or replace such a cookie?
Many thanks!
EDIT:
There isn't much code to show - I access the local cookie, and I can easily catch the exception. But how can I create a fresh shared object at the same location once I caught the exception?
try {
localStorage = SharedObject.getLocal("heywoodsApp");
} catch (err:Error) {
// what do I do here?
}
The error is easily reproduced by damaging the binary content of a Flash cookie with an editor.
I'm not really sure why you'd be getting a range error - esp if you report that can find it. My only guess for something like this is there is a possibility of crossing boundries with respect to the cross-domain policy. Assuming IT has control over where the server is hosted, if the sub-domain ever changed or even access type (from standard to https) this can cause issues especially if the application is ongoing (having been through several releases). I would find it rather hard to believe that you are trying to retrieve a named SO that has already been named by another application - essentially a name collision. In this regard many of us still uses the reverse-dns style naming convention even on these things.
If you can catch the error it should be relatively trivial to recover from: - just declare the variable outside the scope of the try so it's accessible to catch as well. [edit]: Since it's a static method, you may need to create a postfix to essentially start over with a new identifier.
var mySO:SharedObject;
....
catch(e:Error)
{
mySO = SharedObject.getLocal('my.reversedns.so_name_temp_name');
//might want to dispatch an error event or rethrow a specific exception
//to alert the user their "preferences" were reset.
}
You need to be testing for the length of SharedObject and recreate if it's 0. Also, always use flush to write to the object. Here's a function we use to count the number of times our software is launched:
private function usageNumber():void {
usage = SharedObject.getLocal("usage");
if (usage.size > 0) {
var usageStr:String = usage.data.usage;
var usageNum:Number = parseInt(usageStr);
usageNum = usageNum + 1;
usageStr = usageNum.toString();
usage.data.usage = usageStr;
usage.flush();
countService.send();
} else {
usage.data.usage = "1";
usage.flush();
countService.send();
}
}
It's important to note that if the object isn't available it will automatically be recreated. That's the confusing part about SharedObjects.
All we're doing is declaring the variable globally:
public var usage:SharedObject;
And then calling it in the init() function:
usage = SharedObject.getLocal("usage");
If it's not present, then it gets created.
Let's say that I have a canvas component called myCanvas and I instantiated it with
var myCanvasPage:myCanvas = new myCanvas;
this.addChild(myCanvasPage);
Then I want to essentially reload myCanvasPage later on. In effect I want to do this:
this.removeChild(myCanvasPage);
var myCanvasPage:myCanvas = new myCanvas;
this.addChild(myCanvasPage);
except instead of creating a new instance of myCanvas, I want to use the already created instance of myCanvas and essentially reload or re-create it but making sure that the instance name and references to it remain the same. What would be the best way to do this?
Whenever you do
var myCanvasPage:myCanvas = new myCanvas;
you are instantiating the myCanvasPage Object.
Removing an object from the stage will not delete the Object from memory.
As long as there is a reference somewhere in your code the myCanvasPage Object will not be garbage collected and all the values and attributes will be the same as at the time you removed it from the stage.
To make that reference you have to scope it to your class.
public var myCanvasPage:myCanvas = new myCanvas;
So now you would reference it with
this.myCanvasPage
and when you are ready to add it back to the stage.
this.addChild(this.myCanvasPage);
So to recap you can add and remove an Object from stage
this.addChild(this.myCanvasPage);
this.removeChild(this.myCanvasPage);
all day long and the data in that object will never go away.
Some good reading on garbage collection
What do you mean as "reloading"? Maybe it is simpler to create data-driven components and change that data to change or reset component state>
Woa I'm not sure where to start here... I think THE_asMan addresses most of your misunderstandings. The missing bit I think you need to look into is how a reference to an object holds (i.e. is counted) as long as it doesn't go out of scope. Just keep in mind that as long as the a variable is not out of scope, its reference to some object (if there is one, i.e. if it is not null) is counted.
http://help.adobe.com/en_US/ActionScript/3.0_ProgrammingAS3/WS5b3ccc516d4fbf351e63e3d118a9b90204-7f9d.html#WS5b3ccc516d4fbf351e63e3d118a9b90204-7f8c