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My java file is one line of blank spaces? Common solutions haven't worked

I made an account just for this because no existing Stack Overflow question seems to answer this and it's difficult to google this question.
I walked away from my computer for perhaps 45 minutes - when I walked away, my code was fine - and upon return, I saw that my .java source file (I'm using Eclipse) was just one extremely long line of blank spaces. No code visible, but the .java file is still the same 9KB it once was, and I can open it in text editors just fine... except the text editors also show a string of what appear to be blank spaces. No, local history isn't working. What on Earth is going on here? And how do I fix it? Clearly the information still exists somewhere, but how do I access it?
No, I don't have a recent backup. Walk of shame.
Here's an attempt to copy-paste the contents of the file:

Eclipse - renaming a package got rid of a bunch of stuff, is there a way to recover it?

So I made a package, lets call it dev.example.project for example purposes. all my other packages extended off of that one, with names like dev.example.project.handler or dev.example.project.assets. But I decided to go back and change the dev.example.project package's name to something else, like dev.betterexample.project.
I thought it would be a simple matter of renaming all the other packages and import statements so no errors would happen, but right after i changed the name, all the packages in my project turned white and became inaccessible. I changed the name back to what it originally was, but when i opened Eclipse again, some packages and files were simply not there.
I spent a lot of time on this project, someone help?

Depending how exactly you did that renaming, various things could have gone wrong.
Remember: you can always go in and work outside of eclipse. Close it, open a file explorer and create directories that use the names you want to use. Then move files manually to their target directories. If you want to, open them in another text editor and fix the package lines. When you now open eclipse, do a refresh and full rebuild. Things should be fine then.
That is probably not the most elegant solution, but it always works. And more importantly, you are in full control of everything that happens!
And for the record: the real answer to avoid catastrophic loss of code is to use a source code management system such as git. And to then push your changes constantly out to that "backup" facility.

Eclipse suddenly closes Java file, and now refuses to recognize it as such

I've come across quite an odd problem with eclipse.
I was working on a project and I right clicked on a method call declared in another class and used Eclipse's handy find declaration in project (saves me quite a bit of scrolling) to run a search for that specific method declaration. Right as it should my search pane pops up with a link to the method declaration. So I click the link, the other file the method is declared in is opened automatically, and poof the Java file I had searched from disappears from my editor tabs.
So I say to myself, "damn this old version of eclipse (Indigo) has some bugs...now I've got to go reopen my file and get back to my spot...GREAT!". But when I open the file, it is treated like a plain text file. All the text is the same color, and the outline won't work!!!

So I solved the problem whilst I was typing the above up and decided to post the answer since it isn't a nice clean solution..and I doubt one exists.
Okay so file wasn't being recognized by eclipse..
So I open the file and do a Save As, and save it under another name in the same package.
Then, I went to my test code and right clicked on a method call that was declared in the file that eclipse had buggered up, and went to search for declaration in project.
Sure enough two results popped up, one in the newly saved as file, and one in the old one.
I clicked on the old one, and still plain text...no difference.
But then I clicked on the new one, and my highlighting was back!
So then I just deleted the old file and refactored.
I think somehow eclipse made the file disappear without properly closing it...just my guess, glad I resolved this nice and quickly, hopefully anyone who has the same issue can be helped by this.

This happened to me a couple of minutes ago. Trying to close/open the projet, restarting eclipse did not work for me.
The steps I used were:
Pick another Java file (same package) right next to the bogus one (make sure syntax highlighting works on this one)
Choose 'Save As' and override the bogus one.
Verify that the bogus one now has proper syntax highlighting
Use git checkout -- to retrieve you original file
Et voilà !

Java set breakpoints programmatically

Is there any way to programmatically set breakpoints in Java?
Assume you have the filename with the source code line:
Test.java:123
How this can be done?

The Eclipse IDE does not allow you to set a breakpoint from your java code.
However, it does allow you to set conditional breakpoints. With a conditional breakpoint, you can tell Eclipse to only break on a line after some Java expression evaluates to true. You can only tell it to break after some number of iterations. These modes should suffice for almost every usecase.
To enable a conditional breakpoint, right-click on a breakpoint and go to "Breakpoint properties".

Back in the days of VisualAge Jave, I did this with
DebugSupport.halt()
This is something that would have to be supported by the IDE, and would break if the IDE dependencies were not present. As fas I know there are no IDEs today that support this.

I had the same problem but with 10000 files of java which i wanted to search for some string and put breakpoints based on that search.
You can generate xml file containing all breakpoints you need.
How to get that xml file structure?? simply go to debug mode --> right click ->Export breakpoints->then save the file anywhere.open that file and see how it is constructed.
what i did that i searched all the files line by line and generated that xml file and imported it to eclipse.
-You may wonder that how you can loop through 10000 file line by line as it will take a lot of time,you are right but what i did to overcome this is by inserting all lines into indexed field on mysql db.
-I know your case is not that complex but i hope it gives you an idea.you may come with something even better.

Most debuggers will let you break on an exception, so just create your own BreakpointException class, throw and immediately catch it. Have the debugger pause only on BreakpointException.

AutoIndent in Eclipse possible?

I have been wracking my brain trying to figure this out. For the first time I used jEdit the other day and I was pleasantly surprised that it auto indented my code (meaning that I'd put in the following code:
int method () {
_ //<-- and it put me here automatically
I've tried to get the same thing working with eclipse but with no success. I got into the code formatter but I don't see how to make that happen.
Is it possible to do this? Also while I'm here, is there a such thing as a eclipse plugin that will allow you to search the methods and classes of the standard java library?
Thanks

Personally all I use for this is the format options Window->preferences under Java->Code Style ->Formatter.
I once took the time to tweek how I like my code to look like when I work and exported the whole thing. After that I just code without too much bother on what it looks like. When I find the code looks messy by pressing the combination ctrl+shift+f and the whole class becomes pretty again, comments and all.
After a while it pretty much became a reflex...
code code code
ctrl-s, ctrl-b (cause I disable auto build sometimes), ctrl-shift-f
code some more etc...
Once I got used to this I never really cared how it presented the code as i was typing because I knew it would look all pretty as soon as the loop/if/switch/method etc is finished

My clean eclipse install does this by default.
Have you changed any options? Make sure the file you are editing has the .java file extension. The preference options that control the typing automations are under Java -> Editor -> Typing in the Window -> Preferences menu.
Also, I find that the auto-indenting, and most of the other auto-complete functions of eclipse do not function well if the file I am editing has errors in it which prevent compilation. Make sure that your curly-braces are matched correctly, this is the main one that I've noticed blocks auto-indent.
Regarding searching through the standard Java libraries, use the Search -> Java.. menu option, and check the JRE libraries checkbox, then search away. You can also use the Hierarchy view to see how the classes relate. Also, in the Package and Project views you can expand the JRE System Library, and then expand rt.jar which holds pretty much all the standard Java pacakges.

Eclipse has always done this for me by default.
One really cool thing about eclipse is that you can search preference pages. Just right click and go to prefrences. Go to the "Window" menu, and click "Prefrences". Then at the top of the tree view there's a text box that says "type filter text". Replace that with "indent" and it should bring up the page where the indent option is.
Make sure that eclipse recognizes your file as a java file, that you're using the Java distribution, the latest version, etc.

Iv been trying to work around the eclipse indenting and other supposed features for years, and it seems that the bottom line is this ...
It only works for the programming style of the authors, so to use it you need to modify your style to comply.
This would be OK except that the authors of eclipse have some very strange ideas about common shortcut keys.
One horrid example is the search features, eg when did Ctrl+K become "Find Next occurrence" and why doesnt F3 or n work?
That all being said I use eclipse because if you have the time to wait around while it starts up - or never close it - and you can modify everything youve learned about using an editor - why why why - then it will certainly increase your efficiency.
Please note that there is a preference setting for indenting, it can be set for a project, a workspace, or globally, but no matter how you set it eclipse will still chuck tab characters in where you dont want them.
In fact its indent crazy, like it wants to indent everything, even if its already indented.
Like I said Iv been using it for years and it STILL drives me nuts with its random behavior.

Follow these steps for Eclipse:
Select all text: ctrl+A
Correct indentation: ctrl+I

You should check:
Hidden features/tricks for Eclipse?
What is your favorite hot-key in Eclipse?