1. IO Lecture 5

2. Everything is streams … almost In Java Input/Output is mainly stream based In java.io : Console I/O File I/O One Exception: RandomAccessFile not a stream Raw byte or multi byte characters. Later we will look at java.nio “nio”=New IO

3. A stream is …sequential by nature Data is considered to be one contiguous (one dimensional) group of information from beginning to end.

4. Dual stream hierarchies in Java Byte-oriented vs character-oriented Byte orientation has the longest history Internationalization movement induced (during the 90’s) a need for multibyte characters. Byte-oriented classes java.io.OutputStream java.io.InputStream Character-oriented classes java.io.Writer java.io.Reader

5. Stream Trees

6. Reader Tree

7. Writer Tree

8. Byte oriented streams Read chapter 3. See figure 3-1 p158. A few special streams: ByteArrayInputStream lets you read an array of byte as though it were an InputStream object SequenceInputStream/-OutputStream makes it possible to concatenate data from two or more InputStream objects into a single stream. PipedInputStream/-OutputStream implements one half of a “pipe”. Pipes are very useful when communicating between threads. See also chapter 11.

9. Character-oriented streams Most Byte stream classes has a corresponding character stream class. E.g. FileReader FileInputStream FileWriter FileOutputStream Figure 3-9 p177 Adapter classes for Byte oriented data E.g. InputStreamReader takes an InputStream object and converts it into a Reader -object.

10. Commonly Used Readers and Writers FileReader: read text from files BufferedReader: wraps around other Readers to get whole lines of text at a time FileWriter: write files PrintWriter: println method automatically adds newline and flushes

11. Common Uses of java.io Writing to System.out (a PrintStream) Reading from System.in (an InputStream) public static void main(String[] args) throws IOException { System.out.println("What's your favorite ice-cream flavor?"); InputStreamReader isr = new InputStreamReader(System.in); BufferedReader br = new BufferedReader(isr); String userInput = br.readLine(); System.out.println(userInput + " isn't an ice-cream flavor!"); }

12. Writing a file The long way to get a writer FileOutputStream fos = new FileOutputStream("test1"); OutputStreamWriter writer = new OutputStreamWriter(fos); The short way to get a writer FileWriter writer = new FileWriter(fileName); After getting a writer writer.write("This is a test file.\n"); writer.write("Hello World.\n"); writer.write("Goodbye World.\n"); writer.close();

13. Reading a file The long way to get a reader FileInputStream fis = new FileInputStream(fileName); InputStreamReader reader = new InputStreamReader(fis); The short way to get a reader FileReader reader = new FileReader(fileName); After getting a reader BufferedReader br = new BufferedReader(reader); String s = br.readLine(); while (s != null) { System.out.println(s); s = br.readLine(); } reader.close();

14. java.nio New: Buffer management Channels File locking Memory mapping

15. java.nio: Buffers “Buffer” a well-known concept, but is often home brewed by developers. They are now predefined and performance- optimized. See figure 3-10 p179. ByteBuffer, CharBuffer, DoubleBuffer, FloatBuffer, IntBuffer, LongBuffer, MappedByteBuffer, ShortBuffer

16. java.nio: Channels A flexible concept that includes any open connection to a program entity. DatagramChannel : when working with datagram sockets (UDP). SocketChannel : for use with TCP/IP sockets. FileChannel : for reading, writing, mapping, manipulating files. Pipe.SinkChannel/-SourceChannel : for use with the writable/readable end of a pipe. For more info: read code examples in the book or on the web. See figure 3-12 p183.

17. java.nio: Memory mapping MappedByteBuffer We may map the contents of a file into a region of memory. File locking necessary See figure 3-13 p186-187.

18. Collections Lecture 5

19. Programming… The foundation in programming is connecting well-known algorithms with well-known data structures. Hopefully the resulting program is easy to maintain.

20. Three basic interfaces Collection The root interface of the collection framework. Set Does not allow duplicate elements May be ordered. E.g. HashSet, TreeSet, LinkedHashSet. List Defines standard behavior for ordered collections (i.e. sequences). May contain duplicates. E.g. LinkedList, ArrayList, Vector, Stack.

21. Collection traversal You traverse a collection with an “Iterator”, which is a cursor object. An object that guides you through the collection sequentially. (hasNext(), next()…) Very simple, and very safe. You don’t instantiate an Iterator, by calling some constructor. You kindly ask for it. (Remember the “Factory” design pattern?) Iterator it = someCollection.iterator(); while (it.hasNext()){ Item I = (Item) it.next(); } Notice that the it object is declared to implement the Iterator interface. We don’t really know from which class the object is instantiated.

22. Maps Does not extend the “Collection” interface Base class for (Key -> value) datatypes Unsorted Map implementations E.g. LinkedHashMap, HashMap (fastest), Sorted implementations TreeMap,

23. The new Collections framework vs the old legacy framework The new framework of Collection based classes (since Java 2), adopts the Iterator interface. Older legacy classes use the Enumeration interface, which is similar to Iterator. Iterator Enumeration: iterator() elements() hasNext() hasMoreElements() next() nextElement()

24. Thread safety The legacy collections are somewhat thread safe (but not alltogether) since the methods are fully synchronized (for good and for worse). The Collections framework is not thread-safe for efficiency reasons. If multiple threads may access it, the collection may be wrapped in a readOnlyCollection or synchronizedCollection Collections.synchronizedCollection(Collection c) Collections.unmodifiableCollection(Collection c) Iterator is strongly promoted in favour of Enumeration. If the collection is modified by another Iterator, you get a ConcurrentModificationException. Iterator is fail-safe. Enumeration is not.

25. Collections class Contains wrappers for thread safety. … also contains algorithms Sort, shuffle, search, max, min, reverse, rotate, swap.

26. Observer/Observable Lecture 5

27. Observer/Observable example public class IntrusionDetector extends Observable { private Random rand = new Random(); public void connect(){ if( rand.nextBoolean() ){ // Intrång setChanged(); notifyObservers(); } public class SysAdm implements Observer { private String name; public SysAdm( String name, IntrusionDetector id ) { this.name = name; id.addObserver(this); } public void update( Observable server, Object err ){ System.out.println( name + " förhindrar intrång"); }

28. Parsing Strings Lecture 5

29. StringTokenizer Java.util Break a string into separate tokens A token may be a word or a symbol Usually a sequence of character not including a whitespace. Token delimiter can be specified, and is default set to whitespaces.

30. Regular expressions A regular expression is a string of characters that describe a sequence of characters as a pattern. The pattern is often a mixture of literals and characters with special meaning. See documentation for “java.util.regex” See figure 4-31, 4-32, 4-33, 4-44 p307-308.

31. RegExp: Basic steps 1. Create a Pattern object that encapsulates an expression. 2. Acquire a CharSequence object that holds the sequence of characters to test. 3. Get a Matcher object 4. Call a method on the Matcher Object. Find(), matches(), group()

32. Only two classes in java.util.regex Pattern Matcher But regular expressions are rich and worthwhile looking into.

33. Remember …to keep an extra eye on the backslashes In literal Java strings the backslash is an escape character. The literal string "\\" is a single backslash. In regular expressions, the backslash is also an escape character. The regular expression \\ matches a single backslash. This regular expression as a Java string, becomes "\\\\". That's right: 4 backslashes to match a single one. Test and confirm your belief