Java I/O Stream Fundamentals

To effectively utilize I/O streams in Java, its recommended to first understand the classification hierarchy and then explore the specific usage of individual stream classes.

Overview

• Input: Reads data from a source (disk or network) into the program's memory.
• Output: Writes data from memory out to a destination (disk or network).

Classification of Streams

1. Byte Input Stream (InputStream): Reads raw byte data from a source into memory.
2. Byte Output Stream (OutputStream): Writes raw byte data from memory to a destination.
3. Character Input Stream (Reader): Reads character data (handling encoding) from a source into memory.
4. Character Output Stream (Writer): Writes character data from memory to a destination.

Byte Streams

Reading Bytes with FileInputStream

The FileInputStream reads raw bytes from a file. Note that reading text byte-by-byte may cause encoding issues (e.g., Chinese characters appearing as garbled text).

Constructors:

• FileInputStream(String path)
• FileInputStream(File fileObj)

Reading Methods:

• int read(): Reads a single byte. Returns -1 at the end of the file.
• int read(byte[] buffer): Reads bytes into an array. Returns -1 at the end.

Example: Reading a single byte:

FileInputStream fis = new FileInputStream("module/data.txt");
int byteVal;
while ((byteVal = fis.read()) != -1) {
    System.out.print((char) byteVal);
}
fis.close();

Example: Reading using a buffer array:

FileInputStream fis = new FileInputStream("module/data.txt");
byte[] chunk = new byte[10];
int bytesRead;
while ((bytesRead = fis.read(chunk)) != -1) {
    String content = new String(chunk, 0, bytesRead);
    System.out.print(content);
}
fis.close();

Example: Loading all bytes: While you can define a massive array matching the file size, or use readAllBytes(), these approaches are risky for large files as they may cause OutOfMemoryError.

FileInputStream fis = new FileInputStream("module/data.txt");
// Option 1: Manual allocation
// byte[] data = new byte[(int) new File("module/data.txt").length()];
// fis.read(data);

// Option 2: Built-in method
byte[] data = fis.readAllBytes();
System.out.println(new String(data));
fis.close();

Writing Bytes with FileOutputStream

This class writes raw bytes to a file.

Constructors:

• FileOutputStream(String path, boolean append): If append is true, data is added to the end of the file.

Writing Methods:

• write(int b)
• write(byte[] b)
• write(byte[] b, int off, int len)

Example:

FileOutputStream fos = new FileOutputStream("module/output.txt", true);

// Write bytes from a string
String message = "Hello Stream\r\n";
fos.write(message.getBytes());

// Write specific bytes
byte[] nums = {65, 66, 67}; // A, B, C
fos.write(nums, 0, 2);

fos.close();

Character Streams

Reading Characters with FileReader

FileReader is suitable for reading text files as it handles character decoding.

Methods:

• int read(): Reads a single character.
• int read(char[] cbuf): Reads characters into an array.

Example: Reading characters:

FileReader fr = new FileReader("module/poem.txt");
char[] charBuffer = new char[8];
int count;
while ((count = fr.read(charBuffer)) != -1) {
    System.out.print(new String(charBuffer, 0, count));
}
fr.close();

Writing Characters with FileWriter

Character streams often require a flush() to ensure data is physically written to the disk before closing.

Methods:

• write(int c)
• write(String str)
• write(char[] cbuf)

Example:

FileWriter fw = new FileWriter("module/log.txt");

fw.write(98); // char 'b'
fw.write("Sample Text");

char[] chars = {'J', 'a', 'v', 'a' };
fw.write(chars);

// Flush to ensure data is written
fw.flush();

// Close stream (automatically flushes)
fw.close();

Buffered Streams

Buffered streams wrap standard streams to improve performance by reducing physical read/write operations using an internal buffer (default 8192 bytes/chars).

Byte Buffered Streams

• BufferedInputStream
• BufferedOutputStream

Example:

FileInputStream fis = new FileInputStream("module/largefile.bin");
BufferedInputStream bis = new BufferedInputStream(fis);

byte[] temp = new byte[100];
int len;
while ((len = bis.read(temp)) != -1) {
    // Process bytes
}
bis.close();

Character Bufffered Streams

• BufferedReader: Offers readLine() method to read text line by line.

Example:

FileReader fr = new FileReader("module/input.txt");
BufferedReader br = new BufferedReader(fr);

String line;
while ((line = br.readLine()) != null) {
    System.out.println(line);
}
br.close();