Streams

Stream means a continuous flow of data. Stream is an object that reads from from a source or write to a destination or both. Used to output to a screen or a read from a keyboard. Used when total memory is lesser than the incoming or outgoing data. Used to process and transmit data progressively.

In Java, streams are used to perform input and output (I/O) operations.

Types

Based on data format

Byte-oriented

Handles data in raw binary format. Used for input and output of 8-bit bytes. In Java, the main classes to work with byte streams are InputStream and OutputStream.

Character-oriented

Handles data in the form of characters (16-bit Unicode). Used for input and output of characters. In Java, the main classes to work with character streams are:

In the below example, output file is written as the input file is being read. This approach can be used to copy a huge file as well.

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class CharacterStreamExample {
    public static void main(String[] args) {
        try (FileReader fr = new FileReader("input.txt");
             FileWriter fw = new FileWriter("output.txt")) {
            int charData;
            while ((charData = fr.read()) != -1) {
                fw.write(charData);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Based on behaviour

Input stream

In Java:

• InputStraem - an abstract class that represents an input stream of bytes. Provides methods to read bytes from a source.
• Reader - an abstract class that represents an input stream of characters. Provides methods to read characters from a source.

Common subclasses of InputStream include:

• FileInputStream for reading from files.
• ByteArrayInputStream for reading from byte arrays.
• BufferedInputStream for buffering input to improve performance.

Common subclasses of Reader and Writer include:

• FileReader for reading from files.
• CharArrayReader for reading from character arrays.
• BufferedReader for buffering input to improve performance.

Output stream

In Java:

• OutputStream - an abstract class that represents an output stream of bytes. Provides methods to write bytes to a destination.
• Writer - an abstract class that represents an output stream of characters. Provides methods to read characters from a source.

Common subclasses of OutputStream include:

• FileOutputStream for writing to files.
• ByteArrayOutputStream for writing to byte arrays.
• BufferedOutputStream for buffering output to improve performance.

Common subclasses of Reader and Writer include:

• FileWriter for and writing to files.
• CharArrayWriter for writing to character arrays.
• BufferedWriter for buffering output to improve performance.

Connection stream

Basic streams that connect directly to the source or destination of data.

Chain stream

A stream that is reads from or writes to a stream. Used to add additional functionality to connection streams. Aka. filtered stream.