Here is the code, i will put remark where is a NullPonerException:
This program should , by my belife, iterate over the whole file system on my computer, and, on my suprise, it does over all items in the root directory, and it even goes further somewhere, where I tried to follow this program with debugger, but with my limited knowledge of how to use the debugger, on Eclipse, I didn't figured out why this program have fallen apart by the NullPointerException on the given marked line.
If I put that line in a try/catch block, then I get as an output few hundart times printed stack trace, not much more, and a number 411288, which is obviously a close number to how much files there is on my computer:
By the way, I'm on Vista.
I can't solve this problem using debugger becaouse I am a begginer in using debugger and becaouse when I put a break line overthere where a NullPointerException ... arises... I end up clicking resume on that place for many times before the first NullPointerException and then when it happenes the program is over and I cant get variables...
Maybe I am suppose to put some code inside catch block that will read to me something saved from the last iteration without exception, from where I could read exact place (file) where I'm stuck.
Maybe someone knows why?
What is this?
(I think that possibly I'm over for today. Some nice days...
I suspect the stack trace is actually pointing to the line before the one you've indicated. File.listFiles() can return null if there's an I/O error; I think that includes security issues -- i.e., if "f" is a directory to which you do not have read access, listFiles() will return null. You need to check for that null, and that should fix your problem. I believe you should be able to use File.canRead() to see if you have read permission first; if canRead() returns false, listFiles() would return null, so you can just skip that directory.
This program is going to eat an awful lot of memory -- why do you need to use a new CompositeDirectory at each recursive call?
1) Yes. stack trace was pointing one line before than what I indicated.
Isn't it that, if there's no real array, just null, that then there shouldn't be no iteration as well?
So there is (at least one iteration) with f1 seted to null... One day I shall understand that.
2) Like this it works:
output : ))))
3) But, like this it doesn't work:
I don't know why it doesn't work. Maybe it cares only for files, maybe it works like that only on unix, maybe it has something to do with the security manager, I don't know for now. I readed javadoc, probably File.canRead() is only for files
4) I am not doing anything practical. I am learning. After all, I am allowed to clog my own computer alone. : )))) I was learning composite pattern. I will invent later some practical usage, maybe... : )))
Thank You very much for Your kind help...
p.s. I found one song from Kylie Minogue that I liked so much that I have listened it for many times now. I'm listening it right now. The name of the song is "Stay this way", from Kylie Minogue. It's good song, if anyone likes: