Advanced JAVA 3

Advanced JAVA 3

Input/Output Streams

Java I/O (Input and Output) is used to process the input and produce the output based on the input.

Java encapsulates Stream under java.io package. Java defines two types of streams. They are,

Byte Stream : It provides a convenient means for handling input and output of byte.

Character Stream : It provides a convenient means for handling input and output of characters. Character stream uses Unicode and therefore can be internationalized.

Byte Stream Classes

Byte stream is defined by using two abstract class at the top of hierarchy, they are InputStream and OutputStream.

These two abstract classes have several concrete classes that handle various devices such as disk files, network connection etc.

Some important Byte stream classes.

Stream class	Description
BufferedInputStream	Used for Buffered Input Stream..
BufferedOutputStream	Used for Buffered Output Stream.
DataInputStream	Contains method for reading java standard datatype
static String format(Locale l, String format, Object... args)	returns formatted string with given localer.
DataOutputStream	An output stream that contain method for writing java standard data type
FileInputStream	Input stream that reads from a file.
FileOutputStream	Abstract class that describe stream input.
OutputStream	Abstract class that describe stream output.
PrintStream	Output Stream that contain print() and println() method.

These classes define several key methods. Two most important are,

read() : reads byte of data.
write() : Writes byte of data.

Character Stream Classes

Character stream is also defined by using two abstract class at the top of hierarchy, they are Reader and Writer. These two abstract classes have several concrete classes that handle unicode character.

Some important Character stream classes

Stream class	Description
BufferedReader	Handles buffered input stream.
BufferedWriter	Handles buffered output stream.
FileReader	Input stream that reads from file.
FileWriter	Output stream that writes to file.
InputStreamReader	Input stream that translate byte to character.
OutputStreamReader	Output stream that translate character to byte.
PrintWriter	Output Stream that contain print() and println() method.
Reader	Abstract class that define character stream input.
Writer	Abstract class that define character stream output.

 

Reading Console Input

We use the object of BufferedReader class to take inputs from the keyboard.

BufferedReader br = new BufferedReader (new InputStreamReader (System.in));

Here,
br is Object of BufferedReader class
InputStreamReader is subclass of Reader class. It converts bytes to character.
System.in - Console inputs are read from this

Reading Characters

read() method is used with BufferedReader object to read characters. As this function returns integer type value has we need to use typecasting to convert it into char type.

int read() throws IOException.

Below is a simple example explaining character input,

class CharRead
{
 public static void main( String args[])
 {
  BufferedReader br = new Bufferedreader(new InputstreamReader(System.in));
  char c = (char)br.read();       //Reading character  
 }
}

Reading Strings

To read string we have to use readLine() function with BufferedReader class's object.

String readLine() throws IOException

Program to take String input from Keyboard in Java.

import java.io.*;
class MyInput
{
 public static void main(String[] args)
 {
  String text;
  InputStreamReader isr = new InputStreamReader(System.in);
  BufferedReader br = new BufferedReader(isr);
  text = br.readLine();          //Reading String  
  System.out.println(text);
 }
}

Program to read from a file using BufferedReader class.

import java.io.*;
class ReadTest
{
 public static void main(String[] args)
 {
  try 
  {
   File fl = new File("d:/myfile.txt");
   BufferedReader br = new BufferedReader(new FileReader(fl)) ;
   String str;
   while ((str=br.readLine())!=null)
   {
    System.out.println(str);
   }
   br.close();
   fl.close();
  }
  catch (IOException  e)
  { e.printStackTrace(); }
 }
}

Program to write to a File using FileWriter class.

import java.io.*;
class WriteTest
{
 public static void main(String[] args)
 {
  try 
  {
   File fl = new File("d:/myfile.txt");
   String str="Write this string to my file";
   FileWriter fw = new FileWriter(fl) ;
   fw.write(str);
   fw.close();
   fl.close();
  }
  catch (IOException  e)
  { e.printStackTrace(); }
 }
}