Files and Streams in Java

1. Files and Streams in Java Written by Amir Kirsh

2. Lesson’s Objectives • By the end of this lesson you will: • Be able to work with Text and Binary streams and files • Be familiar with the character encoding importance for text streams in Java

3. Reading from the standard input • Files and Streams • Binary files • Text files and character encoding • Exercise Agenda

4. Reading from the standard input try { BufferedReader in = new BufferedReader( new InputStreamReader(System.in) ); String str = ""; while (str != null) { str = in.readLine(); System.out.println(str.toUpperCase()); }} catch (IOException e) { }

5. Reading from the standard input • System.in an object of type InputStream • A stream of bytes (NOT chars!) • InputStreamReader • A bridge from byte stream to character stream, can read single chars • BefferedReader • adds the method “readLine”

6. Files and Streams • The File class represents a file or directory • Supports inquiries on the file or dir, operations like replacing its name, and opening it (if it’s a file) to get a stream of bytes for read / write • Stream classes represents a stream of bytes / chars • InputStream • InputStreamReader • BefferedReader • DataInputStream – and more • Streams are not related only to files, we can have a stream of bytes for network sockets, ByteArray or even for a String

7. Scanner Scanner is a helper class for getting input Scanner s = new Scanner(System.in); System.out.println("Please insert a string: "); String str = s.nextLine(); System.out.println("Please insert a number: "); int i = s.nextInt(); // may throw InputMismatchException

8. Binary Files • Binary Files hold data in binary format • DataInputStream / DataOutputStream -- for primitive types • Serialization – using the Serializable interface and the FileInputStream / FileOutputStream readObject() and writeObject() methods -- Class exercise 1: write array of integers to binary file -- Class exercise 2: serialize Hashmap to file

9. Text Files and Character Encoding Joel On SW about character encoding:http://www.joelonsoftware.com/articles/Unicode.html– a must read! • InputStream • A stream of bytes (NOT chars!) • InputStreamReader • A bridge from byte stream to character stream, can read single chars • An important parameter is the Charset • Also when constructing a String out of bytes, it’s important to provide the Charset used on the byte array -- Class exercise: write a string to a text file, as UTF-8, as UTF-16 and as ISO-8859-1, as ISO-8859-8 and as US-ASCII

10. Reading from the standard input • Files and Streams • Binary files • Text files and character encoding • Exercise Agenda

11. Exercise • Write a program that reads numbers from the input stream, separated by EOL (=user presses enter), stopping when something that is not a number is entered. • The program will send the numbers to two different files: • Text file: numbers.txt -- numbers separated by “,” • Binary file: numbers.bin

12. That concludes this chapter amirk at mta ac il