File IO

• File is an abstract data type
• File


  • Can perform the following operations: Create a File, Get File Information, Write to a File, Read from a File, Delete a File
• Java File Class


  An abstract representation of file and directory pathname. A pathname can be either absolute or relative.
• Creating a File Object

  A File object is created by passing in a string that represents the name of a file, or another File object
• Java File Class Methods

  • The File class has a number of methods that allow us to work with and manipulate files on the file system
  • File class cannot modify or access the contents of the file it represents
• Reader Class


  • Used to read the 16-bit characters from the input stream
  • It is an abstract class and can't be instantiated
  • There are various subclasses that inherit the Reader class and override the methods of the Reader class
• Reading a text file in Java

  • There are several ways to read a plain text file in Java
  • Every utility provides something special e.g. BufferedReader provides buffering of data for fast reading, and Scanner provides parsing ability
• Using BufferedReader class


  • Reads text from a character-input stream
  • Uses a buffer for efficient reading of characters, arrays, and lines
  • The buffer size may be specified, or the default size may be used
• Checking End of File/Stream (EOF)


  • readLine() returns null
  • read() returns -1
• Using FileReader class


  • Used for reading character files
  • The constructors of this class assume that the default character encoding and the default byte-buffer size are appropriate
• Creating a FileReader


  • FileReader input = new FileReader(String name)
  • FileReader input = new FileReader(File fileObj)
• Using Scanner class


  • Used if you want to read file line by line or based on some java regular expression
  • Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace
  • The resulting tokens may then be converted into values of different types using the various next methods (nextInt(), nextDouble(),etc)
  • The hasNext() verifies whether the file has another line and the nextLine() method reads and returns the next line in the file
• Using FileInputStream class


  • Used for reading byte-oriented data (streams of raw bytes) such as image data, audio, video etc.
  • Can also read character-stream data

  
• Reading CSV File in Java

  • The CSV stands for Comma-Separated Values
  • The CSV file format is used when we move tabular data between programs that natively operate on incompatible formats
  • The default separator of a CSV file is a comma (,)
  • The BufferedReader class can be used to read it line by line, and the String.split() method can be used to split each line by comma to convert it into columns
• Creating a file


  • To create a file in Java, you can use the createNewFile() method
  • This method returns a boolean value: true if the file was successfully created, and false if the file already exists
  • The method is enclosed in a try...catch block to handle IOException
• Options in Writing to a File

  • FileWriter
  • BufferedWriter
  • PrintWriter
  • FileOutputStream
• FileWriter


  • The simplest way to write a file in Java
  • Writes directly into Files and should be used only when the number of writes is less
• BufferedWriter


  • Almost similar to FileWriter but uses internal buffer to write data into File
  • Must be used when the number of write operations is more
• PrintWriter


  Can be used to write formatted text to a file
• FileOutputStream


  Used for writing byte-oriented data (streams of raw bytes) such as image data, audio, video etc.
• File - a named location used to store related information
• File I/O -

  • File I/O (input/output) means reading and writing the file contents
  • Java uses concept of a stream to make I/O operation fast
  • The java.io package contains all the classes required for input and output operations
• Stream -

  • A series of data is referred to as a stream
  • In Java, Stream is classified into two types:

  1. Byte Stream
  2. Character Stream
• Byte Stream -

  • it is mainly involved with byte data
  • a file handling process with a byte stream is a process which an input is provided and executed with the byte data
• Character Stream -

  • it is mainly involved with character data
  • a file handling process which a character stream is a process in which an input is provided and executed with the character data
• Java File Class -

  • The File Class is an abstract representation of file and directory pathname. A pathname can be either absolute or relative
  • The File class gives us the ability to work with files and directories on the file system
• File Operation in Java -

  • In Java, a File is an abstract data type
  • We can perform the following operations on a file

  1. Create a File
  2. Get File Information
  3. Write to a File
  4. Read from a File
  5. Delete a File
• Creating a File Object - A File Object is created by passing in a string that represent the name of a file, or another file object
• getName()

  • method is used to find the file name
  • return type is String
• createNewFile()

  • method is used to create a new empty file
  • return type is boolean
• delete()

  • method that is used to delete a file
  • return type is boolean
• canRead()

  • method is used to check whether we can read the data of the file or not
  • return type is boolean
• canWrite()

  • method that is used to check whether we can write the data into the file or not
  • return type is boolean
• exists()

  • method that is used to check whether the specified file is present or not
  • return type is boolean
• getAbsolutePath()

  • method is used to get the absolute pathname of the file
  • return type is String
• length()

  • method is used to get the size of the file in bytes
  • return type is long
• Reader Class

  • is is used to read the 16-bit characters from the input stream
  • it is an abstract class and can't be instantiated
  • there are various subclass that inherit the Reader class and override the methods of the Reader class
  • all methods of the Reader class throw an IOException
• CharArrayReader - provided methods to read characters from the char array
• FilterReader - provides methods to read characters from the underlying character input stream
• InputStreamReader - provides methods to convert bytes to characters