File input and output operations in Java are performed using streams. There are two types of streams - byte streams and character streams. Byte streams handle input/output at the byte level while character streams handle input/output at the character level using Unicode encoding. The File class in Java represents files and directories on the filesystem and provides methods to perform operations like creating, reading, updating and deleting files.

1. File I/O

2. File Input and Output Operations:-
 File I/O operations are performed using the concept of streams.
 A stream means a continuous flow of data.
 A stream is a logical container of data that allows us to read from and
write to it.
 The stream-based IO operations are faster than normal IO operations

3. Functionality of java streams

4.  Every Java program creates 3 streams automatically.
 These streams are attached to the console
1. System.out: standard output stream for console output operations.
2. System.in: standard input stream for console input operations.
3. System.err: standard error stream for console error output operations.

5. Example For Streams
1. System.out.println(“hai");
2. System.err.println(“welcome");
int a=System.in.read(); //returns ASCII code of 1st character
System.out.println((char)a); //will print the charact

6. Java provides two types of streams
• 1.Byte Stream
• 2. Character Stream

7. Stream with various built-in classes used by the
java IO system

8. Java Byte Stream
 The java byte stream is defined by two abstract classes
1. InputStream
2. OutputStream.
 The InputStream class used for byte stream based input operations,
 The OutputStream class used for byte stream based output operations.
 The InputStream and OutputStream classes have several classes
to perform various IO operations based on the byte stream.

10. InputStream class
 The InputStream class has defined as an abstract class
 it has the following methods which have implemented by its concrete classes.

11. OutputStream class
 The OutputStream class has defined as an abstract class,
 It has the following methods which have implemented by its concrete classes.

12. i) Reading data using BufferedInputStream
 BufferedInputStream class to read data from the console.
BufferedInputStream(InputStream inputstream)
BufferedInputStream(InputStream inputstream, int bufSize)
 The BufferedInputStream class use a method read( ) to read a
value from the console, or file

13. Ex 1: Reading from console

14. EX2: Reading from a file

15. Writing data using BufferedOutputStream

16. Character Stream in java
 IO stream manages 16-bit Unicode characters, it is called a character stream.
 The Unicode set is basically a type of character set where each character
corresponds to a specific numeric value within the given character set.
 character stream is defined by two abstract classes, Reader and Writer

17.  Reader class used for character stream based input operations
 Writer class used for character stream based output operations
 Reader and Writer classes have several concreate classes to perform
various IO operations based on the character stream.

19. Reader class
 The Reader class has defined as an abstract class
 the following methods implemented by its concrete classes

21. Writer class
 The Writer class has defined as an abstract class.
 It has the following methods implemented by its concrete classes.

23. Reading data using BufferedReader
 BufferedReader class to read data from the console.
 The BufferedInputStream class needs InputStreamReaderclass.
 The BufferedReader use a method read( ) to read a value from the console,
or file, or socket.

24. Example 1 - Reading from console
import java.io.*;
public class ExReading
{
public static void main(String[] args) throws IOException
{
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader in = new BufferedReader(isr);
String name = "";
System.out.print("Please enter your name: ");
name = in.readLine();
System.out.println("Hello, " + name + "!");

25. Example 2 - Reading from a file
import java.io.*;
class ExReading
{
public static void main(String[] args) throws IOException
{
Reader in = new FileReader(“c/abc.txt”);
try
{
char c = (char)input.read();
System.out.println("Data read from a file - '" + c + "'");
}
catch(Exception e) {
System.out.println(e);
}
finally {
input.close();

26. Writing data using FileWriter
import java.io.*;
public class ExWriting
{
public static void main(String[] args) throws IOException
{ Writer out = new FileWriter("C:Desktopcse.txt");
msg = "cse";
try
{
out.write(msg);
System.out.println("Writing done!!!");
}
catch(Exception e)
{ System.out.println(e); }
finally
{ out.close(); }
}} }

27. Writing from a Binary File
 DataOutputStream and DataInputStream enable you to write or read primitive data to or from a
stream.
 They implement the DataOutput and DataInput interfaces,
 DataOutputStream extends FilterOutputStream, which extends OutputStream.
 DataOutputStream defines the following constructor:
DataOutputStream(OutputStream outputStream)
DataOutput defines methods
 final void writeDouble(double value) throws IOException
 final void writeBoolean(boolean value) throws IOException
 final void writeInt(int value) throws IOException

28. Reading from a Binary File
 DataInputStream is the complement of DataOuputStream. It extends FilterInputStream,which
extends InputStream, and it implements the DataInput interface.
DataInputStream(InputStream inputStream)
Methods:
 double readDouble( ) throws IOException
 boolean readBoolean( ) throws IOException
 int readInt( ) throws IOException

29. File Class
 File is a built-in class in Java.
 File class has been defined in the java.io package.
 The File class represents a reference to a file or directory.
 File class has various methods to perform operations like creating a file or directory,
reading from a file, updating file content, and deleting a file or directory.

30. File class constructors

31. File class Methods
1. boolean canExecute() : Tests whether the application can execute the file denoted by this
abstract pathname.
2. boolean canRead() : Tests whether the application can read the file denoted by this abstract
pathname.
3. boolean canWrite() : Tests whether the application can modify the file denoted by this abstract
pathname.
4. int compareTo(File pathname) : Compares two abstract pathnames lexicographically.
5. boolean createNewFile() : Atomically creates a new, empty file named by this abstract pathname
.
6. static File createTempFile(String prefix, String suffix) : Creates an empty file in the default
temporary-file directory.

32. 8) boolean exists() : Tests whether the file or directory denoted by this abstract pathname exists.
9) String getAbsolutePath() : Returns the absolute pathname string of this abstract pathname.
10) long getFreeSpace() : Returns the number of unallocated bytes in the partition .
11) String getName() : Returns the name of the file or directory denoted by this abstract pathname.
12) String getParent() : Returns the pathname string of this abstract pathname’s parent.
13) File getParentFile() : Returns the abstract pathname of this abstract pathname’s parent.
14) String getPath() : Converts this abstract pathname into a pathname string.
15) boolean isDirectory() : Tests whether the file denoted by this pathname is a directory.

33. File
import java.io.File;
class FileDemo {
static void p(String s) {
System.out.println(s);
}
public static void main(String args[]) {
File f1 = new File("/java/COPYRIGHT");
p("File Name: " + f1.getName());
p("Path: " + f1.getPath());
p("Abs Path: " + f1.getAbsolutePath());
p("Parent: " + f1.getParent());
p(f1.exists() ? "exists" : "does not exist");
p(f1.canWrite() ? "is writeable" : "is not writeable");
p(f1.canRead() ? "is readable" : "is not readable");
p("is " + (f1.isDirectory() ? "" : "not" + " a directory"));
p(f1.isFile() ? "is normal file" : "might be a named pipe");
p(f1.isAbsolute() ? "is absolute" : "is not absolute");
p("File last modified: " + f1.lastModified());
p("File size: " + f1.length() + " Bytes");
}
}

34. File
Output
File Name: COPYRIGHT
Path: /java/COPYRIGHT
Abs Path: /java/COPYRIGHT
Parent: /java
exists
is writeable
is readable
is not a directory
is normal file
is absolute
File last modified: 812465204000
File size: 695 Bytes

35. Creating File using File class
import java.io.*;
class ExFile
{
public static void main(String[] args)
{
try {
File file = new File(“c/abc.txt");
if (file.createNewFile())
{
System.out.println("New File is created!");
} else
{
System.out.println("File already exists.");
}
} catch (IOException e)
{
e.printStackTrace();
}
}

36. List out all files in a directory or path
import java.io.*;
class ExFileList
{
public static void main(String[] args)
{
File f=new File(“c:/abc/cse");
String filenames[]=f.list();
for(String filename:filenames)
{
System.out.println(filename);
}
}
}