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JAVA File IO/Streams

Learning objectives

• Understand basic principles of File I/O
• Understand and be able to use File I/O exceptions
• Be able to write out to a text file in the desired format
• Be able to read in text from a file

What is Java IO?

• Java I/O means Input and Output.
• It helps Java programs read data (input) and write data (output).
• java has java.io.package for IO operations
• java.io.package also helps with file handling

What is stream?

• Stream is a sequence of data or like a pipe that carries data.
• Java has default 3 streams created and attached to the console
• System.out,System.in,System.err
• A stream is composed of bytes.
• Closing a stream when it's no longer needed.

Text I/O

• A File object encapsulates the properties of a file or a path, but does not contain the methods for reading/writing data from/to a file.
• You need to create objects using appropriate Java I/O classes.
• File input -reading data from files
• File output- writing data to files

The File Class

• Provides the template for File objects that allow abstraction of the file and path names
• Wrapper class for filename and directory path
• Does not provide the ability to read from or write to files
• Github code sample FileClass

Writing to a File

• We use FileWriter to write "Hello, Java! I love coding!" into a file called myFile.txt.
• Github code sample FileClass

Reading From a File

• Github code sample FileClass

Java I/O Categories

• The classes in the I/O package divide input and output streams into other categories
• An I/O stream is either a. Character Streams: For working with text data (like words and sentences).
• Byte Streams: For working with binary data (like images and audio files).
• Java I/O API provides Interfaces for reading files
• Streams: Used to read binary data
• Readers: Used to read character/text Example: FileReader (reads characters from a file).
• FileReader: Reads in characters
• BufferedReader: Buffering of data for faster reading
• Scanner: provides parsing ability Scanner (reads and processes text from a file or keyboard).

BufferedReader

• Uses a buffer to allow the reading of full lines of text at a time rather than one byte at a time
• Github code sample BufferedReader

Scanner

• Creates a Scanner object to read data from the specified file
• Scanner object has several methods
• Java.util.Scanner package
• Github code sample Scanner

Writing Data To a File

1. FileWriter:

   • Used for basic file writing.

   • Writes characters or strings directly to a file.

   • Example: Writing a simple text file.

2. BufferedWriter:

   • Writes data to a file more efficiently by using an internal buffer.

   • Reduces the number of direct writes to the file, improving performance.

   • Example: Writing large amounts of data.

3. PrintWriter:
   • Provides formatted writing (like System.out.println).
   • Makes it easy to write data in a human-readable format.

   • Example: Writing structured data (e.g., CSV files).

FileWriter

• Writes text to character files using a default buffer size
• The FileWriter is meant for writing streams of characters
• Github code sample FileWriter

BufferedWriter

                        br = 	new BufferedReader(new FileReader(f));
                        bw = 	new BufferedWriter(new FileWriter(f));	
                        s = 	br.readLine()	Returns next input line without newline char(s) or null if no more input. May throw IOException.
                        s = 	br.close()	Close when finished reading to unlock file.	
                        bw.writeLine(s)	Writes s to file without newline char(s). May throw IOException.
                        bw.newLine()	Writes operating-system dependent newline (CR, LF, or CRLF).
                        bw.close()	Call close() when finished writing, otherwise data may not be written to disk.                 	
                    

BufferedWriter

• Writes text to a character-output stream, buffering characters so as to provide for the efficient writing of single characters, arrays, and strings.
• Github code sample BufferedWriter

PrintWriter

• Prints formatted representations of objects to a text-output stream.
• This class implements all of the print methods found in PrintStream.
• Github code sample PrintWriter

FileOutputStream

• A file output stream is an output stream for writing data to a File or to a FileDescriptor.
• FileOutputStream is meant for writing streams of raw bytes such as image data. For writing streams of characters, consider using FileWriter.
• Github code sample FileOutputStream

Java NIO

1. Non-Blocking I/O:
   • Allows a thread to perform other tasks while waiting for I/O operations to complete.
   • Example: A thread can read data from a file while simultaneously performing other computations.
2. Channels and Buffers:
   • Channels are like pipes that connect to I/O sources (e.g., files, sockets).
   • Buffers are containers for data, used to read from or write to channels.
3. Files API:
   • Provides utility methods for file operations, such as reading, writing, copying, and deleting files.
   • Simplifies common file tasks compared to the traditional java.io package.
• Github code sample NIO methods

Example: Non-Blocking I/O with Channels and Buffers

• Github code sample NonBlockingExample

Thank you