1. File Handling

2. System class
□ System class has three attributes
□ in (System.in)
□ Object of class InputStream
□ out (System.out)
□ Object of OutputStream
□ err (Error Stream)
□ Object of ErrorStream

3. Introduction
□ We need to have some method of
storing data permanently – even when
the computer is switched off and
program has been terminated
□ We need to store multiple records,
each consist of multiple fields in a file

4. File Handling
□ Java provide File streams – Input and
Output streams that handle
communication between main
memory and named file on a disk
□ We can write data to a file in the form
of Strings, lines of text or basic types
such as integers or characters.
□ Java even allows us to store and
retrieve whole objects

5. A file on a disk or tape can be a text
file or a binary file.

6. The standard input and output behave
like text files.

7. The standard error behaves like
a text file.

8. StreamS

11. File streams are created, connected to
files, and disconnected from files by
the programmer.

12. Input and Output
□ Input
□ Allowing information to come in from outside
world
□ Transfer of data from some external device to
main memory
□ Output
□ Display or storage of processed information
□ Transfer of data from main memory to an
external device
□ In order to have Input and Output , a channel of
communication is required referred to as a stream
□ We have standard input and output stream which
is keyboard and screen
□ We have standard error stream which is also set to
screen

13. One of the most frequently used
task in programming is writing to
and reading from a file. To do
this in Java there are more
possibilities.

14. Encoding
□ Java supports three different ways of
encoding data
□ Text
□ Data on disk is stored as characters in the form used by
external system
□ ASCII normally but as java uses UNICODE so internally
some transformation do happen
□ Readable by text editor
□ Binary
□ Data is stored in same format as the internal
representation of the data used by the program to
store data so number 107 will be stored as 1101011.
□ Cannot be properly read by text editor
□ Object
□ Whole object can be written

15. Reading and writing to text files
Writing to a File Reading from a File
FileWriter name = new Filereader name = new
FileWriter(“Filename”); FileReader(“Filename”);
PrintWriter printname = new BufferedReader buffername
PrintWriter(name); = new
BufferedReader(name);
printname.println(data );
String str =
buffername.readLine();
Printname.close();
If(str == null) => End of File
Buffername.close();

16. Filename handling
□ To write anything to a file first of all we
need a file name we want to use.
□ The file name is a simple string like:
□ String fileName = "test.txt";
□ If you want to write in a file which is
located elsewhere you need to define
the
complete file name and path in your
fileName variable:
□ String fileName = "c:filedemotest.txt";

17. Open a file
□ To open a file for writing use the FileWriter class
and create an instance from it.
The file name is passed in the constructor like
this:
□ FileWriter writer = new FileWriter(fileName);
□ This code opens the file in overwrite mode. If
you want to append to the file then
you need to use an other constructor like this:
□ FileWriter writer = new
FileWriter(fileName,true);
□ Besides this the constructor can throw an
IOException so we put all of the code inside
a try-catch block.

18. Write to a File
□ At this point we have a writer object and we can
send real content to the file.
□ Do this using the write() method, which has more
variant but the most commonly used requires a
string as input parameter.
□ Calling the write() method doesn't mean that it
immediately writes the data into the file.
□ The output is maybe cached so if you want to
send your data immediately to the file you need
to call the flush() method.
□ As last step you should close the file with the close()
method and you are done

21. Reading from a File
□ reading from a file is very similar to writing.
□ We only need to use *Reader objects
instead of *Writer objects.
□ It means that you can use FileReader or
BufferedReader.
□ A simple FileReader can handle only a single
character or a character array it is more
convenient to use the BufferedReader which can
read a complete line from a file as a string.
□ So using a BufferedReader we can read a text
file line by line with the readln() method

22. return fileContent.toString();

23. Reading and Writing to Binary
Files
□ FileOutputStream and
DataOutputStream
□ FileInputStream and DataInputStream
□ If will try to access something after end
of file, it will throw and EOFException

24. Reading and writing to Binary files
Writing to a File Reading from a File
FileOutputStream out = new
FileOutputStream("c:test.
txt",true);
DataOutputStream dataOut =
new
DataOutputStream(out);
String str ="Saira Anwar";
dataOut.writeBytes(str);
dataOut.close();