Java Development

[Schwoebel]

I believe wait() and notify() is what I want to use.  But I could be wrong.  I don't know.  I'm not sure.  So I will ask.

I am trying to do an update process on an App when it starts up.  What I want it to do is to creat a new directory, finish, create another directory within the just-made directory, finish, then download a file to the first directory, and then download a series of files to the second-created directory.

 sort of like this

create /file/

create /file/fileinFile/

Download fileX to file

Download files to /file/fileinFile/

Pop a new screen

all at the click of one button on the front screen of the page.

When I do it bare, just like that, the first file gets created but the runtime debugger is all ready trying to create the second file before the other one is done being built.  Throwing a runtime exception.

I've been doing a lot of research on the issue and I come to think that I need to do it with Wait()'s and Notify()'s.  Even through reading about it, my head is spinning.

I can tell you that when run separately all of the methods im trying to do run successfully.

It's only when I try to get them to run consecutively that I get errors.

I have a code sample of the bare item above:

public class Updater implements Runnable
{
		FolderMaker Folders = new FolderMaker("file:///SDCard/file/");
		FolderMaker pFolder = new FolderMaker("file;///SDCard/file/fileinFile/");
		FileListDownload Filelist = new FileListDownload();
		XMLfileDownloader XML = new XMLfileDownloader();
		
	public Updater() 
	{
		this.run();
		
	}

	public void run() {
		
		Folders.run();
		pFolder.run();
		Filelist.run();
		XML.run();
		UiApplication.getUiApplication().pushScreen(new TestMenuScreen());

	}
		
}

 This Class is called from a MainScreen button listener using invokeandwait.

Any sample code to help me do this, or maybe a 3-year old (lol) level explanation would be greatly appreciated.

[simon_hain]

wait blocks the current thread, it should never be used from the event thread.

creating folders and other file operations are I/O and should be done in a separate thread.

you can use a so-called sync-object for wait and notify. it is a complicated topic, but you can use all references available about desktop java to learn more about it.

[Schwoebel]

So this wouldn't work

pFolder.wait();

Folders.run();

pFolder.notify();

[simon_hain]

no, it makes no sense

[Schwoebel]

Can you think of a simpler way to accomplish what I'm trying to do? (assuming you understand what I want to do)

Can you or anyone else make any other suggestions?

[simon_hain]

creating files or folders are blocking operations, the control flow continues after it has finished.

put it all into a separate thread, i don't see the need for wait/notify

[Alan_Hollis]

As Simon stated.

public class Updater implements Runnable
{

		
	public Updater() 
	{
		this.run();
		
	}

	public void run() 
	{
		FolderMaker Folders = new FolderMaker();
		Folders.makeFolder("file:///SDCard/file/");
		Folders.makeFolder("file;///SDCard/file/fileinFile/");
		
		FileListDownload Filelist = new FileListDownload();
		XMLfileDownloader XML = new XMLfileDownloader();
	}
		
}

There's no need to create two other FolderMakers threads. Same goes with the FileListDownload and XML fileDownloader.

[Schwoebel]

After making the folders, I need to download an XML file to the first file.  Then I need to parse the XML file that I downloaded and download information based on that.

I figured out the folders. and have the XML downloaded, but it's skipping over step where it parses the Downloaded XML file and does more downloads off of that.

[jtp5120]

http://download.oracle.com/javase/tutorial/essential/concurrency/guardmeth.html

Please read through Guarded Blocks, I've implememented a similar idea but with JSON data and a SQLite database.

[arkadyz]

In order to achieve what you need, you have to:

1) On the click of a button, create a separate Thread with all blocking operations inside its run() method (don't do anything blocking in the constructor or member initializations - those are executed in the event thread). Start that thread.

2) Also, push a "Please, wait..." screen which will have no user interaction (maybe let the user cancel the whole operation, but I would postpone that until you have the first iteration working).

3) At the very end of your background Thread's run() method, push your new screen (wrap the pushScreen in invokeLater - otherwise it won't work).