Reader Classes
Introduction
-
Readeris an abstract class used to read character-oriented data (16-bit Unicode) from input sources such as files, memory, or network connections. -
It is present in the
java.iopackage. -
It provides basic methods like
read()to read single characters, arrays of characters or lines of text from input sources. -
Unlike
InputStreamwhich deals with bytes,Readeris specifically designed to handle characters, making it suitable for text data.
-
Below is the diagram for Reader class hierarchy:
- Each of these subclasses are designed for specific purposes, which are explained below one by one.
1. BufferedReader
- Description: Reads text from a character input stream efficiently by buffering characters, thus reducing the number of I/O operations.
- Use in Projects: Commonly used to read text files line by line.
-
Example Syntax:
BufferedReader br = new BufferedReader(new FileReader("file.txt")); String line = br.readLine(); br.close();
2. LineNumberReader
-
Description: A subclass of
BufferedReaderthat keeps track of line numbers while reading characters. - Use in Projects: Useful when you need to know the line number while reading files (like compilers or log readers).
-
Example Syntax:
LineNumberReader lnr = new LineNumberReader(new FileReader("file.txt")); String line = lnr.readLine(); int lineNumber = lnr.getLineNumber(); lnr.close();
3. CharArrayReader
- Description: Allows reading characters from a character array as a stream.
- Use in Projects: Useful for testing or when data is already available in a character array.
-
Example Syntax:
char[] data = {'J','a','v','a'}; CharArrayReader car = new CharArrayReader(data); int ch = car.read(); car.close();
4. FilterReader
- Description: An abstract class for filtering character streams, usually extended to add custom functionalities.
- Use in Projects: Rarely used directly; helpful when you need to create a custom filter (e.g., to modify characters while reading).
-
Example Syntax:
// FilterReader is abstract, must be extended // Example: PushbackReader is one implementation
5. PushbackReader
-
Description: A subclass of
FilterReaderthat allows characters to be pushed back into the stream. - Use in Projects: Useful in parsers when you need to “unread” characters for reprocessing.
-
Example Syntax:
PushbackReader pr = new PushbackReader(new FileReader("file.txt")); int ch = pr.read(); pr.unread(ch); // pushes back the character pr.close();
6. InputStreamReader
- Description: A bridge between byte streams and character streams. Reads bytes and decodes them into characters using a specified charset.
-
Use in Projects: Commonly used with
System.infor reading user input as characters. -
Example Syntax:
InputStreamReader isr = new InputStreamReader(System.in); int ch = isr.read(); isr.close();
7. FileReader
-
Description: A convenient subclass of
InputStreamReaderfor reading character files. - Use in Projects: Simplifies reading character files without manually specifying encoding (uses platform default).
-
Example Syntax:
FileReader fr = new FileReader("file.txt"); int ch = fr.read(); fr.close();
8. PipedReader
-
Description: Reads characters from a connected
PipedWriter, used for communication between threads. - Use in Projects: Useful in multithreaded applications for inter-thread communication.
-
Example Syntax:
PipedWriter pw = new PipedWriter(); PipedReader pr = new PipedReader(pw); // one thread writes to pw, another reads from pr
9. StringReader
- Description: Reads characters from a string as a stream.
- Use in Projects: Useful when working with text data already available as a string.
-
Example Syntax:
StringReader sr = new StringReader("Hello Java"); int ch = sr.read(); sr.close();
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