Java Streams

Streams

• A stream is a sequence of data. 
• In Java, a stream is composed of bytes. 
• It's called a stream because it is a continuous flow of data. 

Use of I/O Streams:

The primary use of I/O streams is to perform data transfer between a Java program and an external entity or another part of the same program. Common use cases include:

• File Operations: Reading data from files and writing data to files.
• Network Communication: Sending and receiving data over network connections (using Sockets which provide InputStream and OutputStream).
• In-Memory Data Handling: Treating byte arrays or character arrays as sources or destinations of data.
• Data Conversion: Converting between byte streams and character streams using specified encodings.
• Buffering: Improving the efficiency of I/O operations by reading or writing data in larger chunks.
• Data Formatting: Writing formatted output using PrintStream and PrintWriter.
• Object Persistence: Saving the state of Java objects to storage and restoring them later using object serialization streams.
• Inter-Thread Communication: Allowing threads within the same program to exchange data using piped streams.

Character Streams:

• Abstract Base Classes:

  • Reader: Represents an input stream of characters. Provides methods for reading characters.
  • Writer: Represents an output stream of characters. Provides methods for writing characters.

• Common Concrete Implementations:

• File I/O:
  • FileReader: Reads characters from a file (uses the default character encoding).
  • FileWriter: Writes characters to a file (uses the default character encoding).
• Memory I/O:
  • CharArrayReader: Reads characters from a character array in memory.
  • CharArrayWriter: Writes characters to a character array in memory.
  • StringReader: Reads characters from a String.
  • StringWriter: Writes characters to a String buffer.
• Buffered I/O (for efficiency):
  • BufferedReader: Adds buffering to a character input stream, reading characters in larger chunks and providing line-reading capabilities (readLine()). Often wraps other Reader implementations.
  • BufferedWriter: Adds buffering to a character output stream, writing characters in larger chunks and providing a newLine() method. Often wraps other Writer implementations.
• Character Encoding Conversion:
  • InputStreamReader: An adapter that converts a byte input stream (InputStream) into a character input stream (Reader) using a specified character encoding.
  • OutputStreamWriter: An adapter that converts a character output stream (Writer) into a byte output stream (OutputStream) using a specified character encoding.
• Print Writer (for formatted character output):
  • PrintWriter: Adds functionality to print formatted representations of various data values as characters. It's similar to PrintStream but operates on character streams.
• Piped Streams (for inter-thread character communication):
• PipedReader: The receiving end of a character pipe.
• PipedWriter: The sending end of a character pipe.

Byte Streams:

• Abstract Base Classes:

  • InputStream: Represents an input stream of bytes. It provides methods for reading bytes from a source.
  • OutputStream: Represents an output stream of bytes. It provides methods for writing bytes to a destination.

• Common Concrete Implementations:

• File I/O:
  • FileInputStream: Reads bytes from a file.
  • FileOutputStream: Writes bytes to a file.
• Memory I/O:
  • ByteArrayInputStream: Reads bytes from a byte array in memory.
  • ByteArrayOutputStream: Writes bytes to a byte array in memory.
• Buffered I/O (for efficiency):
  • BufferedInputStream: Adds buffering to an input stream, reading data in larger chunks. Often wraps other InputStream implementations.
  • BufferedOutputStream: Adds buffering to an output stream, writing data in larger chunks. Often wraps other OutputStream implementations.
• Data Conversion:
  • DataInputStream: Reads primitive Java data types (int, float, boolean, etc.) from an underlying input stream in a machine-independent way.
  • DataOutputStream: Writes primitive Java data types to an underlying output stream in a machine-independent way.
• Object Serialization:
  • ObjectInputStream: Reads Java objects that were previously serialized.
  • ObjectOutputStream: Writes Java objects in a serialized format.
• Piped Streams (for inter-thread communication):
  • PipedInputStream: The receiving end of a pipe.
  • PipedOutputStream: The sending end of a pipe.
• Filtering Streams (for data transformation):
  • FilterInputStream: An abstract class that provides a basis for filtering input streams (e.g., BufferedInputStream, DataInputStream).
  • FilterOutputStream: An abstract class that provides a basis for filtering output streams (e.g., BufferedOutputStream, DataOutputStream).
• Print Stream (for formatted output):
• PrintStream: Adds functionality to print formatted representations of various data values. System.out and System.err are instances of PrintStream.