ISE 582: Web Technology for Industrial Engineering

1. ISE 582: Web Technology for Industrial Engineering University of Southern California DJE Dept of Industrial and Systems Engineering Lecture 6 JAVA Cup 5: Data Structures

2. Handouts • Lecture 6 slides • READ Winston & Narasimhan : • Chapters 27-31, 33 (pp 149-194, 201-203) Web Technology for IE

3. JAVA Cup 5 • File Access • Input file streams • Output file streams • Arrays and Vectors • How to create and access arrays • Expandable vectors • Characters and Strings Web Technology for IE

4. File Input Streams • Reading files one-byte-at-a-time • Taking bigger bites • Java’s input-output package • Traditional string handling • Updating to tokens: number / words Web Technology for IE

5. File input streams • A stream is a sequence of values. • To read bytes from a file: • FileInputStreamstream = newFileInputStream(“input.data”) • FileInputStreamstream = newFileInputStream(“~username/public_html/ise582/input.data”); • When you are done, it is good to: • stream.close() • Reads ONE BYTE AT A TIME… Web Technology for IE

6. To take bigger bites than bytes • To read characters from your file: • InputStreamReaderreader = newInputStreamReader(stream); • To read lines from your file: • BufferedReaderbuffer = newBufferedReader(reader); • buffer.readLine() stream reader buffer Web Technology for IE

7. Input-output package • Notify JAVA that you want to work with input or output streams: • import java.io.FileInputStream • import java.io.* • In the event of error • use try-catch statements • throw an exception, throwsIOException Web Technology for IE

8. Traditional Approach Example import java.io.*; public class Demonstrate { public static void main(String argv[]) throwsIOException { FileInputStreamstream = new FileInputStream(“input.data”); InputStreamReaderreader = new InputStreamReader(stream); BufferedReaderbuffer = new BufferedReader(reader); String line; while ((line=buffer.readLine())!=null && !line.equals(“”)) { System.out.println(“Line read: “ + line); } stream.close(); return; }} Web Technology for IE

9. String Methods • line.trim() • removes white space • line.indexOf(“ “) • index of first occurrence, starts from 0 • line.substring(2) • returns rest of line after index 2 • line.substring(0,1) • Integer.parseInt(“4”) • converts string to integer Web Technology for IE

10. Example Continued line = line.trim(); int nextSpace = line.indexOf(" "); int x = Integer.parseInt(line.substring(0,nextSpace)); line = line.substring(nextSpace).trim(); nextSpace=line.indexOf(" "); int y = Integer.parseInt(line.substring(0,nextSpace)); line = line.substring(nextSpace).trim(); int z = Integer.parseInt(line); System.out.println("Numbers read: " + x + ", " + y + ", " + z); Web Technology for IE

11. The Token Approach • The stream tokenizer: • StreamTokenizertokens = newStreamTokenizer(reader); • Do away with the BufferedReader • Divides character sequences into tokens, delimited by white space • Token Methods: • tokens.nextToken() • assigns value to nval, tokens.nval • always a double, if need recasting: (int) tokens.nval • end of token string indicated by TT_EOF: tokens.TT_EOF Web Technology for IE

12. Token Example import java.io.*; public class Demonstrate { public static void main (String argv[]) throws IOException { FileInputStream stream = new FileInputStream("input.data"); InputStreamReader reader = new InputStreamReader(stream); StreamTokenizertokens = new StreamTokenizer(reader); while (tokens.nextToken()!= tokens.TT_EOF) { int x = (int) tokens.nval; tokens.nextToken(); int y = (int) tokens.nval; tokens.nextToken(); int z = (int) tokens.nval; Movie m = new Movie(x,y,z); System.out.println("Rating: " + m.rating()); } stream.close(); }} Web Technology for IE

13. Words vs. Numbers • If the token is a number • nextToken returns a TT_NUMBER instance • the number is assigned to nval • If the token is a word • nextToken returns a TT_WORD instance • the number is assigned to sval Web Technology for IE

14. Word / Number Example int next=0; while ((next=tokens.nextToken())!= tokens.TT_EOF) { switch (next) { casetokens.TT_WORD: break; casetokens.TT_NUMBER: int x = (int) tokens.nval; tokens.nextToken(); int y = (int) tokens.nval; tokens.nextToken(); int z = (int) tokens.nval; Movie m = new Movie(x,y,z); System.out.println("Rating: " + m.rating()); break; } } Web Technology for IE

15. Arrays and Vectors • Creating / assigning values to arrays • Passing arrays to methods • Command-line arguments • Creating vectors • Vector methods • Vectors as targets • Using vector iterators Web Technology for IE

16. Creating Arrays • Creating an array • <elt_type><array_name>[] = new<elt_type>[ <size>]; • int durations [] = new int [4]; • What you can do with an array • call / assign an elt: <array_name> [<index>] • find its length: <array_name>.length • Arrays of class instances • <Class><array_name>[] = new<Class>[<size>]; • Movie movies [] = new Movie [4]; Web Technology for IE

17. Instance Array Elements • Field-selection operator still works • movies[3].script = 6 • Checking to see if element is assigned • movies[2] == null • Using instance as target for method • movies[1].rating() Web Technology for IE

18. Mixing Creation and Elt Insertion public class Demonstrate { public static void main (String argv[]) { Movie movies[] = { new Movie(5,6,3), new Movie(8,7,7), new Movie(7,2,2), new Movie(7,5,5)}; int sum = 0; for (int counter=0; counter < movies.length; ++counter) { sum += movies[counter].rating(); } System.out.print("The average rating of the " + movies.length); System.out.println(" movies is " + sum / movies.length); } } Web Technology for IE

19. Arrays and Memory • Arrays are reference type variables • Integer arrays contain a length variable and 4 bytes of memory per instance • Class instance arrays contain a length variable and several bytes for the address of each instance Web Technology for IE

20. Higher Dimension Arrays • You can easily define arrays of higher dimension • double 2DArray[] [] = new double[2][100]; Web Technology for IE

21. Passing an Array to a Method • To designate that a parameter is array • public static Movie[] readData(Movie movies []) throws IOExc.. • public static Movie[] readData(Movie[] movies) throws IOExc.. • E.g.: put file-reads into Auxiliary Class • Some ways to define readData: • Create array, pass array address to method, return address • Create array, pass array address to method, return nothing • Create array variable, pass filename to method, return array Web Technology for IE

22. Command-Line Arguments • The main methods has one parameter • an array of Strings, argv[] • argv.length is # command-line arguments Web Technology for IE

23. Example public class Command { public static void main(String argv[]) { Movie m = new Movie(Integer.parseInt(argv[0]), Integer.parseInt(argv[1]), Integer.parseInt(argv[2])); System.out.println("The rating is " + m.rating()); } } Web Technology for IE

24. Vectors • Vectors vs. Arrays • variable in length • insertions can occur at any point • elements can only be class instances • Provided by Java’s utility package • import java.util.* • Vector v = new Vector(); Web Technology for IE

25. Vector Methods • Insertions and deletions • v.addElement(m) … adds to back end of vector • v.insertElementAt(m,0) … adds to front of vector • v.removeElementAt(0) … removes first element • v.setElementAt(m,4) … replaces element • Access to elements • v.firstElement() • v.lastElement() • v.elementAt(2) • Size of Vector • v.size() Web Technology for IE

26. A Little Quiz • Which methods do you need to represent FIFO queues? • Which methods do you need to represent LIFO queues (stacks)? Web Technology for IE

27. Vectors as Targets • All vector elements are instances of the Object class • All vector methods work with instances of the Object class • You can work with an element of the vector class by casting the element: • ( (Movie)(v.firstElement()) ).rating() Web Technology for IE

28. Example import java.io.*; import java.util.*; public class Auxiliaries2 { public static Vector readData(String fileName) throws IOException { FileInputStream stream = new FileInputStream(fileName); InputStreamReader reader = new InputStreamReader(stream); StreamTokenizer tokens = new StreamTokenizer(reader); Vector v = new Vector(); while (tokens.nextToken() != tokens.TT_EOF) { int x = (int) tokens.nval; tokens.nextToken(); int y = (int) tokens.nval; tokens.nextToken(); int z = (int) tokens.nval; v.addElement(new Movie(x,y,z)); } stream.close(); return v; }} Web Technology for IE

29. Iterators • An iterator maintains a pointer to a place on the parent vector • To create an iterator • Iterator i = v.iterator() • Some Iterator methods • i.next() … returns element, advances pointer • i.hasNext() Web Technology for IE

30. Example import java.io.*; import java.util.*; public class Demonstrate { public static void main(String argv[]) throws IOException { Vector mainVector = Auxiliaries2.readData("input.data"); int size = mainVector.size(); for ( Iterator i = mainVector.iterator(); i.hasNext(); ) { System.out.println(( (Movie) i.next() ).rating()); } } } Web Technology for IE

31. Working with Char & Strings • What you can do with Strings • Specifying delimiters in File-reads Web Technology for IE

32. The String s • s.length() … compare this to arrays • + concatenates two strings • s.charAt(0) extracts first character • s.charAt(0)==‘M’ … note single quotes • switch(s) … use in switch statements • char c = s.charAt(0); • default character is ‘\u000’ Web Technology for IE

33. Example (excerpt) while (tokens.nextToken() != tokens.TT_EOF) { String codeString = tokens.sval; tokens.nextToken(); int x = (int) tokens.nval; tokens.nextToken(); int y = (int) tokens.nval; tokens.nextToken(); int z = (int) tokens.nval; switch (codeString.charAt(0)) { case 'M': v.addElement(new Movie(x,y,z)); break; case 'S': v.addElement(new Symphony(x,y,z)); break; } } Web Technology for IE

34. Specifying Delimiters • To advise the tokens tokenizer to use double quotation marks to delimit strings: • tokens.quoteChar((int) ‘”’) • To tell the tokenizer to recognize carriage returns: • tokens.eolIsSignificant(true); Web Technology for IE

35. Example (excerpt) tokens.quoteChar((int) '"'); tokens.eolIsSignificant(true); Vector v = new Vector(); while (tokens.nextToken() != tokens.TT_EOF) { String nameString = tokens.sval; tokens.nextToken(); int x = (int) tokens.nval; tokens.nextToken(); int y = (int) tokens.nval; tokens.nextToken(); int z = (int) tokens.nval; Movie m = new Movie(x,y,z); m.title = nameString; if (tokens.nextToken() == tokens.TT_EOL) {} else { m.poster = tokens.sval; tokens.nextToken(); } v.addElement(m); } Web Technology for IE

36. Working with O/p File Streams • To connect to output file • FileOutputStreamstream = newFileOutputStream(“output.data”); • To write more than 1-byte-at-a-time • PrintWriterwriter = new PrintWriter(stream); • It’s good to flush out buffered characters • writer.flush() • Close the file • stream.close() Web Technology for IE

37. Example (part) import java.io.*; import java.util.*; public class Demonstrate { public static void main(String argv[]) throws IOException { FileOutputStreamstream = new FileOutputStream("output.data"); PrintWriterwriter = new PrintWriter(stream); Vector mainVector = Auxiliaries4.readData("input3.data"); int size = mainVector.size(); for (Iterator i = mainVector.iterator(); i.hasNext();) { Movie m = (Movie) i.next(); m.writeToFile(writer); writer.println(m.rating()); } writer.flush(); stream.close(); System.out.println("File written"); }} Web Technology for IE