Develop Reference

Opening a file in using java

I'd like to have it so that my java executeble will open a text file up when a Jbutton is pressed.
I dont know where to start so if someone could just nudge me in right direction that would be great
when is searched for opening a file using java it was all about reading in data from a file

Opening a File Pointer:
File f = new File("/path/to/file.txt");
Opening a file input stream (For reading):
FileInputStream in = new FileInputStream("/path/to/file.txt");
Opening a file output stream (for writing):
FileOutputStream out = new FileOutputStream("/path/to/file.txt");
Please take better care to use the documentation and Google. Stack Overflow is not here to do your homework for you.
Edit:
To appease #Takendarkk, I've included this:
Random Access File (More advanced that the previous functions, it opens a file with the mannerisms which C/C++ would use.):
RandomAccessFile raf = new RandomAccessFile("/path/to/file.txt", "rw+");

How to change back to standard output console?

I tried to PrintStream to a text file for writing a bunch of output to a file.
But after the file is created, I was trying to switch back to the standard output just to continue on with other processes, but I have no idea about doing that switch. Seems like I have to setOut to the standard console, but how do I do that?
Below is the code that I used to output to a text file. Any ideas?
PrintStream out = new PrintStream(fistr);
System.setOut(out);
Thanks.

Why don't you save it before modifying it, so that you can go back?
PrintStream standard = System.out;
PrintStream out = new PrintStream(fistr);
System.setOut(out);
/*
some other stuff
*/
System.setOut(standard);

Clear contents of a file in Java using RandomAccessFile

I am trying to clear the contents of a file I made in java. The file is created by a PrintWriter call. I read here that one can use RandomAccessFile to do so, and read somewhere else that this is in fact better to use than calling a new PrintWriter and immediately closing it to overwrite the file with a blank one.
However, using the RandomAccessFile is not working, and I don't understand why. Here is the basic outline of my code.
PrintWriter writer = new PrintWriter("temp","UTF-8");
while (condition) {
writer.println("Example text");
if (clearCondition) {
new RandomAccessFile("temp","rw").setLength(0);
// Although the solution in the link above did not include ',"rw"'
// My compiler would not accept without a second parameter
writer.println("Text to be written onto the first line of temp file");
}
}
writer.close();
Running the equivalent of the above code is giving my temp file the contents:(Lets imagine that the program looped twice before clearCondition was met)
Example Text
Example Text
Text to be written onto the first line of temp file
NOTE: writer needs to be able to write "Example Text" to the file again after the file is cleared. The clearCondition does not mean that the while loop gets broken.

You want to either flush the PrintWriter to make sure the changes in its buffer are written out first, before you set the RandomAccessFile's length to 0, or close it and re-open a new PrintWriter to write the last line (Text to be written...). Preferably the former:
if (clearCondition) {
writer.flush();
new RandomAccessFile("temp","rw").setLength(0);

You'll be lucky if opening the file twice at the same time works. It isn't specified to work by Java.
What you should do is close the PrintWriter and open a new one without the 'append' parameter, or with 'append' set to 'false'.

Write to External File without ending the program

I have a program that is only meant to be terminated by pressing Ctrl + C. In this program I write to an external file using:
File logFile = new File("output.txt");
PrintWriter log_file_writer = new PrintWriter(logFile);
log_file_writer.println("TEXT");
However because I don't know when the program will be terminated, I can't close the file using:
log_file_writer.close();
I think this is resulting in no text appearing in the output file.
Would anyone have a solution for this?
Thank you for your help.

log_file_writer.flush();
will push the content to disk

As the javadoc says:
PrintWriter(File file) Creates a new PrintWriter, without automatic line flushing, with the specified file.
Therefore, you need to flush the data you want to print that is actually buffered:
log_file_writer.flush();

You did not flush the content, I always use the autoFlush argument, but it is not available with File:
PrintWriter log_file_writer = new PrintWriter(new FileOutputStream("output.txt"),true);
but you can also use log_file_writer.flush(); after each write.

Read / write program in Java using JFileChooser

How would I link the file choosen from a JFileChooser to a file and how would I convert it to string being able to display and edit it in a TextArea?
I have the GUI set up using swing, but the link between actionListener and the JFileChooser is not complete.
Any help would be much appreciated.
Code: http://pastebin.com/p3fb17Wi
EDIT: I found this program, that does pretty much what i wanted to, but it does not allow me to save the actual file : http://www.java-forums.org/new-java/8856-how-get-content-text-file-write-jtextarea.html

To be able to save the changes you have made, you will have to use a Save Dialog. In the example you have quoted, a File Open Dialog is used. They work in a similar way, all that you need to do is then get the file to which the user would like to store the changes made, open a stream to it and write the data back. This tutorial shows you how to use the various File Choosers.

All text components support a read(...) and write(...) method. So all you have to do is get the name of the File and create your FileReader or FileWriter and then invoke the method.
All the file chooser is used for is the get the File name to be used by the reader or writer. So the basic code would be:
File saveFile = chooser.getSelectedFile();
FileWriterr writerr = new FileWriter( saveFile );
textArea.write(writer)
Of course you will probably want to use a Buffered reader/writer.