Reading Text from the Standard
Input
Standard Streams:
Standard Streams are a feature provided by many operating systems. By
default, they read input from the keyboard and write output to the
display. They also support I/O operations on files.
Java also supports three Standard Streams:
- Standard Input: Accessed through System.in which
is used to read input from the keyboard.
- Standard Output: Accessed through System.out
which is used to write output to be display.
- Standard Error: Accessed through System.err which
is used to write error output to be display.
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These objects are defined automatically and do not need to be opened explicitly.
Standard Output and Standard Error, both are to write
output; having error output separately so that the user may read error
messages efficiently.
InputStreamReader
inp = new InputStreamReader(system.in);
Working with Reader classes:
Java
provides the standard I/O facilities for reading text from either the file or
the
keyboard on the command line. The Reader class is used for this purpose
that is available in the java.io package. It acts as an abstract
class for reading character streams. The only methods that a
subclass must implement are read(char[], int, int) and close().
the Reader class is further categorized into the subclasses.
The following diagram shows a class-hierarchy of
the java.io.Reader class.
However, most subclasses override some of the methods in order to
provide higher efficiency, additional functionality, or both.
InputStreamReader:
An InputStreamReader is a bridge from byte streams to character streams
i.e. it reads bytes and decodes them into Unicode characters according
to a particular platform. Thus, this class reads characters from a byte
input stream. When you create an InputStreamReader, you specify an
InputStream from which, the InputStreamReader reads the bytes.
The syntax of InputStreamReader is written as:
InputStreamReader
<variable_name> = new InputStreamReader(system.in)
BufferedReader :
The BufferedReader class is the subclass of the
Reader class. It reads character-input
stream data from a memory area known as a buffer maintains
state. The buffer size may be
specified, or the default size may be used that is large enough for text
reading purposes.
BufferedReader converts an unbuffered
stream into a buffered stream using the wrapping expression, where
the unbuffered stream object is passed to the constructor for a buffered
stream class.
For example the constructors of the BufferedReader
class shown as:
BufferedReader(Reader in):Creates
a buffering character-input stream that uses a default-sized input
buffer.
BufferedReader(Reader in, int sz): Creates a buffering character-input stream that uses an input buffer of the specified size. |
BufferedReader class
provides some standard methods to perform specific reading
operations shown in the table. All methods throws an IOException,
if an I/O error occurs.
| Method |
Return Type |
Description |
| read( ) |
int |
Reads a single character |
| read(char[] cbuf, int off, int len) |
int |
Read characters into a portion of an array. |
| readLine( ) |
String |
Read a line of text. A line is considered to
be terminated by ('\n'). |
| close( ) |
void |
Closes the opened stream. |
This program
illustrates you how to use standard input stream to read the user input..
import java.io.*;
public class ReadStandardIO{
public static void main(String[] args) throws IOException{
InputStreamReader
inp = new InputStreamReader(System.in)
BufferedReader br = new BufferedReader(inp);
System.out.println("Enter text : ");
String str = in.readLine();
System.out.println("You entered String : ");
System.out.println(str);
}
}
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Output of the Program:
C:\nisha>javac ReadStandardIO.java
C:\nisha>java ReadStandardIO
Enter text :
this is an Input Stream
You entered String :
this is an Input Stream
C:\nisha> |
Download this example
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