IO_file_handling

I/O Streams

• Streams are one-directional
• package: java.io
• Abstract classes:
  1. InputStream // moves bytes around
  2. OutputStream // moves bytes around
  3. Reader // moves character around, have UTF handling
  4. Writer // moves character around, have UTF handling

• Uses:
  • Reading Writing files in program
  • Taking user input from console
  • Communicating through sockets
• InputStream: FileInputStream, ByteArrayInputStream etc.
• OutputStream: FileOutputStream, ByteArrayOutputStream etc.

Buffer

• A buffer is a container for a fixed amount of data of a specific primitive type.
• In addition to its content a buffer has:
  • position: index of the next element to be read or written
  • limit: which is the index of the first element that should not be read or written.

Program to read/write data from console

public class PersonCreator {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		System.out.print("Enter name, age and phone number: ");
		String name = scanner.next();
		int age = scanner.nextInt();
		Long phoneNumber = scanner.nextLong();
		Person person = new Person(name, age, phoneNumber);
	}
}

Program to read/write file

• BufferedReader is synchronized and can be safely used in multithreaded application
• BufferedReader is faster than Scanner
• Scanner tokenizes the input and uses it

public class BufferedReaderExample {
	public static void main(String[] args) {
		File myFile = new File("example.txt");
		try {
			BufferedReader reader = new BufferedReader(new FileReader(myFile));
			String line;
			while ((line = reader.readLine()) != null) {
				System.out.println(line);
			}
		} catch (IOException ex) {
 
		}
	}
}

Try with resources

• try with resources can be used on classes (called resource) which implements AutoClosable interface. Here BufferedReader and StringWriter are resources.
• It automatically closes resources to prevent memory leaks

public class TryWithResourcesExample {
	public static void main(String[] args) {
		File myFile = new File("example.txt");
		try (
			BufferedReader reader = new BufferedReader(new StringReader("Hello World"));
			StringWriter writer = new StringWriter();
		) {
			
			writer.write(reader.ReadLine());
			System.out.println(writer.toString());
		} catch (IOException ex) {
 
		}
	}
}