Object-Oriented Design and Programming (Java)

2 Topics Covered Today 3.1 Input and Output Programming –3.1.0 Java I/O Stream –3.1.1 File I/O –3.1.2 Using File I/O in the Library System

3 Java I/O Stream What is an I/O stream? Types of Streams Stream class hierarchy Control flow of an I/O operation using Streams Byte streams Character streams Buffered streams Standard I/O streams Data streams Object streams File class

4 What is an I/O Stream? An I/O Stream represents an input source or an output destination A stream can represent many different kinds of sources and destinations –disk files, devices, other programs, a network socket, and memory arrays Streams support many different kinds of data –simple bytes, primitive data types, localized characters, and objects

5 I/O Streams No matter how they work internally, all streams present the same simple model to programs that use them –A stream is a sequence of data

6 Input Stream A program uses an input stream to read data from a source (a file, memory, a socket), and reads the information sequentially, one item at a time.

7 Output Stream A program uses an output stream to write data to a destination, and writing the information out sequentially, one item at time.

8 Types of Streams General Stream Types –Character and Byte Streams Character vs. Byte –Input and Output Streams Based on source or destination –Node and Filter Streams Whether the data on a stream is manipulated or transformed or not

9 Character and Byte Streams Byte streams –For binary data –Root classes for byte streams: The InputStream Class The OutputStream Class Both classes are abstract –Classes of Byte Streams InputStream 、 OutputStream FileInputStream 、 FileOutputStream PipedInputStream 、 PipedOutputStream ByteArrayInputStream 、 ByteArrayOutputStream FilterInputStream 、 FilterOutputStream DataInputStream 、 DataOutputStream BufferedInputStream 、 BufferedOutputStream

10 Character and Byte Streams Character Streams –For Unicode characters –Root classes for character streams The Reader class The Writer class Both classes are abstract –Most programs should use readers and writers to read and write textual information. Reader 、 Writer InputStreamReader 、 OutputStreamWriter FileReader 、 FileWriter CharArrayReader 、 CharArrayWriter PipedReader 、 PipedWriter FilterReader 、 FilterWriter BufferedReader 、 BufferedWriter StringReader 、 StringWriter

11 Input and Output Streams Input or source streams –Can read from these streams –Root classes of all input streams: The InputStream Class The Reader Class Output or sink (destination) streams –Can write to these streams –Root classes of all output streams: The OutputStream Class The Writer Class

12 Node and Filter Streams Node streams (Data sink stream) –Contain the basic functionality of reading or writing from a specific location –Types of node streams include files, memory and pipes Filter streams (Processing stream) –Layered onto node streams between threads or processes –For additional functionality- altering or managing data in the stream Adding layers to a node stream is called stream chaining (stream 链 )

13 java.io hierarchies

14 Abstract Classes InputStream & OutputStream Reader & Writer

15 InputStream Abstract Class Read data from InputStream ： –int read( ); Reads the next byte of data from the input stream –int read( byte b[ ] ); Reads some number of bytes from the input stream and stores them into the buffer array b. –int read( byte b[ ], int off, int len ); Reads up to len bytes of data from the input stream into an array of bytes. –int available( ); Returns the number of bytes that can be read Close Stream ： –close( ); Closes this input stream and releases any system resources associated with the stream.

16 InputStream Abstract Class

17 Node InputStream Classes

18 Filter InputStream Classes

19 OutputStream Abstract Class Write data: –void write( int b ); Writes the specified byte to this output stream. –void write( byte b[ ] ); Writes b.length bytes from the specified byte array to this output stream –void write( byte b[ ], int off, int len ); Writes len bytes from the specified byte array starting at offset off to this output stream. Close stream ： –close( ); Buffer flush: –flush( ); Flushes this output stream and forces any buffered output bytes to be written out.

20 Node OutputStream Classes

21 Filter OutputStream Classes

22 The Reader Class Read character(s) –public int read() throws IOException; –public int read(char cbuf[]) throws IOException; –public abstract int read(char cbuf[],int off,int len) throws IOException; Close reader –public abstract void close() throws IOException;

23 The Reader Class

24 Node Reader Classes

25 Filter Reader Classes

26 The Writer Class Write character(s) to output stream –public void write(int c) throws IOException ； –public void write(char cbuf[]) throws IOException ； –public abstract void write(char cbuf[],int off,int len) throws IOException ； –public void write(String str) throws IOException ； –public void write(String str,int off,int len) throws IOException ； Flush –flush( ) Close stream –public abstract void close() throws IOException ；

27 Node Writer Classes

28 Filter Writer Classes

29 Control Flow of an I/O operation ReadingWriting 1.Create a stream object and associate it with a data-source 2.Give the stream object the desired functionality through stream chaining 1.Create a stream object and associate it with a data-destination 2.Give the stream object the desired functionality through stream chaining 3.while (there is more information) 4. read next data from the stream4. write next data to the stream 5.close the stream

30 Byte Stream Programs use byte streams to perform input and output of 8-bit bytes All byte stream classes are descended from InputStream and OutputStream There are many byte stream classes –FileInputStream and FileOutputStream

31 When Not to Use Byte Streams? Byte Stream represents a kind of low-level I/O that you should avoid –If the data contains character data, the best approach is to use character streams –There are also streams for more complicated data types Byte streams should only be used for the most primitive I/O All other streams are based on byte stream

32 Example: FileInputStream & FileOutputStream

33 Example: FileInputStream & FileOutputStream

34 Character Stream The Java platform stores character values using Unicode conventions Character stream I/O automatically translates this internal format to and from the local character set. –In Western locales, the local character set is usually an 8-bit superset of ASCII. All character stream classes are descended from Reader and Writer As with byte streams, there are character stream classes that specialize in file I/O: FileReader and FileWriter.

35 Example: FileReader & FileWriter

36 Example: FileReader & FileWriter

37 InputStreamReader & OutputStreamWriter public InputStreamReader(InputStream in); –processing stream –reads bytes from an InputStream and converts them to characte public InputStreamReader(InputStream in,String enc) throws UnsupportedEncodingException; –charset decoder –ISO ， UTF-8 ， UTF-16 public OutputStreamWriter(OutputStream out); –Processing stream –converts characters to bytes public OutputStreamWriter(OutputStream out,String enc) throws UnsupportedEncodingException;

38 Line-oriented I/O

39 Buffered Stream Why Buffered Streams? –An unbuffered I/O means each read or write request is handled directly by the underlying OS This can make a program much less efficient, since each such request often triggers disk access, network activity, or some other operation that is relatively expensive. –To reduce this kind of overhead, the Java platform implements buffered I/O streams Buffered input streams read data from a memory area known as a buffer; the native input API is called only when the buffer is empty Similarly, buffered output streams write data to a buffer, and the native output API is called only when the buffer is full.

40 How to create Buffered Streams? A program can convert a unbuffered stream into a buffered stream using the wrapping idiom –A unbuffered stream object is passed to the constructor for a buffered stream class –Example inputStream = new BufferedReader( new FileReader("xanadu.txt")); outputStream = new BufferedWriter( new FileWriter("characteroutput.txt"));

41 Buffered Stream Classes BufferedInputStream and BufferedOutputStream create buffered byte streams BufferedReader and BufferedWriter create buffered character streams

42 Flushing Buffered Streams It often makes sense to write out a buffer at critical points, without waiting for it to fill. This is known as flushing the buffer. Some buffered output classes support autoflush, specified by an optional constructor argument. –When autoflush is enabled, certain key events cause the buffer to be flushed –For example, an autoflush PrintWriter object flushes the buffer on every invocation of println or format. To flush a stream manually, invoke its flush method –The flush method is valid on any output stream, but has no effect unless the stream is buffered.

43 BufferedReader & BufferedWriter Create buffered stream –public BufferedReader(Reader in); use the default buffer size –public BufferedReader(Reader in, int sz); –public BufferedWriter(Writer out); –public BufferedWriter(Writer out, int sz); BufferedReader –public String readLine() throws IOException; Read a line of text BufferedWriter –public void newLine() throws IOException; Write a line separator.IOException

44 Standard Streams on Java Platform Three standard streams –Standard Input, accessed through System.in –Standard Output, accessed through System.out –Standard Error, accessed through System.err These objects are defined automatically and do not need to be opened System.out and System.err are defined as PrintStream objects

45 Data Streams Data streams support binary I/O of primitive data type values (boolean, char, byte, short, int, long, float, and double) as well as String values All data streams implement either the DataInput interface or the DataOutput interface DataInputStream and DataOutputStream are most widely- used implementations of these interfaces

46 DataOutputStream DataOutputStream can only be created as a wrapper for an existing byte stream object

47 DataInputStream Like DataOutputStream, DataInputStream must be constructed as a wrapper for a byte stream End-of-file condition is detected by catching EOFException, instead of testing for an invalid return value

48 Object Streams Object streams support I/O of objects –Like Data streams support I/O of primitive data types –The object has to be Serializable type The object stream classes are ObjectInputStream and ObjectOutputStream –These classes implement ObjectInput and ObjectOutput, which are subinterfaces of DataInput and DataOutput –An object stream can contain a mixture of primitive and object values

49 Input and Output of Complex Object The writeObject and readObject methods are simple to use, but they contain some very sophisticated object management logic –This isn't important for a class like Calendar, which just encapsulates primitive values. But many object contain references to other objects. If readObject is to reconstitute an object from a stream, it has to be able to reconstitute all of the objects the original object referred to. –These additional objects might have their own references, and so on.

50 WriteObject The writeObject traverses the entire web of object references and writes all objects in that web onto the stream –A single invocation of writeObject can cause a large number of objects to be written to the stream.

51 I/O of multiple referred-to objects Object a contains references to objects b and c, while b contains references to d and e

52 Close Streams Always Close Streams –Closing a stream when it's no longer needed is very important — so important that your program should use a finally block to guarantee that both streams will be closed even if an error occurs –This practice helps avoid serious resource leaks.

53 Example: Closing File BufferedReader fileIn = new BufferedReader(new FileReader(filename)); PrintWriter fileOut = new PrintWriter(new FileWriter(filename));... fileIn.close(); fileOut.close();

54 Topics Covered Today 3.1 Input and Output Programming –3.1.0 Java I/O Stream –3.1.1 File I/O –3.1.2 Using File I/O in the Library System

55 The java.io.File Class Either a directory or a file Constructor: –File(String pathname) –File(File parent, String child) –File(String parent, String child) File does not read and write, streams will handle the read or write from/to a file.

56 Create java.io.File Class File(String pathname) File(File parent, String child) File(String parent, String child) File Dir = new File(“d:\\ssd3"); File FullFilename = new File(Dir, "FileDemo.raw "); File f1 = new File("d:/ssd3/unit 3/DirList/."); File f2 = new File(".");

57 Listing Files import java.io.*; import java.util.*; public class DirList { public static void main(String[] args) { File path = new File("."); String[] list; System.out.println(path.getAbsolutePath()); list = path.list(); for (int i = 0; i < list.length; i++) System.out.println(list[i]); }

58 Other File Methods canRead() canWrite() exists() getParent() isDirectory() isFile() lastModified() length()

59 File Methods for Modifying createNewFile() delete() makeDir() makeDirs() renameTo() setLastModified() setReadOnly()

60 FileInputStream Create a FileInputStream –public FileInputStream(String name) –public FileInputStream(File file) FileNotFoundException is thrown if –the named file does not exist, –it is a directory rather than a regular file, –for some other reason cannot be opened for reading Closes this file input stream and releases any system resources associated with the stream

61 FileInputStream Example import java.io.*; class MainClass { public static void main(String args[])throws Exception{ // 1. Create File object FileInputStream inFile=new FileInputStream("c:\\test.txt"); // 2. Create Reader Object to read the text BufferedReader reader=new BufferedReader( new InputStreamReader(inFile)); // 3. Read data String strLine; while((strLine=reader.readLine())!=null) System.out.println(strLine); reader.close(); inFile.close(); }

62 FileOutputStream Create File Object Create FileOutputStream Write data –os.write(byte [ ] b) java.io.File file = new java.io.File("C:\\test.txt"); java.io.OutputStream os = new java.io.FileOutputStream(file);

63 FileOutputStream Example byte[] Data = new byte[100]; java.io.File file = new java.io.File("C:\\test.txt "); try{ java.io.OutputStream os = new FileOutputStream(file); try { os.write(Data); } catch(java.io.IOException e) { } } catch (java.io.FileNotFound e) { }

64 FileReader FileReader(File file) FileReader(String fileName) // 1. Create Reader Object to read the text BufferedReader reader = new BufferedReader( new FileReader("c:\\test2.txt")); // 2. Read data line by line String strLine; while((strLine = reader.readLine()) != null) System.out.println(strLine); reader.close();

65 FileWriter Again, basically the same. The constructors are –FileWriter(File file) –FileWriter(String fileName) –FileWriter(String fileName, boolean append) The last one allows appending, rather than writing to the beginning (and erasing an existing file!). These will create files!

66 File I/O Example Program description: –It first prompts the user for two file names, the name of an input file and the name of an output file, and then copies the contents of the input file to the output file.

67 CopyFile.java import java.io.*; public class CopyFile { private static BufferedReader stdIn = new BufferedReader( new InputStreamReader(System.in)); private static PrintWriter stdOut = new PrintWriter( System.out, true); private static PrintWriter stdErr = new PrintWriter(System.err, true);

68 CopyFile.java public static void main(String[] args) throws IOException { stdErr.print("Source filename: "); stdErr.flush(); BufferedReader input = new BufferedReader( new FileReader(stdIn.readLine())); stdErr.print("Destination filename: "); stdErr.flush(); PrintWriter output = new PrintWriter(new FileWriter(stdIn.readLine())); String line = input.readLine(); while (line != null) { output.println(line); line = input.readLine(); } input.close(); output.close(); stdOut.println("done"); } }

69 Random-Access file RandomAccessFile allow you to read/write data beginning at the a specified location –a file pointer is used to guide the starting position –it supports both input and output with both bytes and characters Methods of Interface DataInput: –readBoolean( ) –readInt( ) –readLine( ) Method of Interface DataOutput: –writeChar( ) –writeDouble( )

70 Using a Random Access File import java.io.*; public class RAFDemo { public static void main(String[] args) { try { File f = new File(“filename"); RandomAccessFile raf = new RandomAccessFile(f, "rw"); // Read a character char ch = raf.readChar(); // Seek to end of file raf.seek(f.length()); // Append to the end raf.writeChars("aString"); raf.close(); } catch (IOException e) { } }

71 File Stream The file streams read or write from a file on the native file system File Streams –FileReader –FileWriter –FileInputStream –FileOutputStream

72 Topics Covered Today 3.1 Input and Output Programming –3.1.0 Java I/O Stream –3.1.1 File I/O –3.1.2 Using File I/O in the Library System

73 Add More Features The data for the library catalog will be stored in a data file and the library system will load the catalog from that file. –catalog.datcatalog.dat The data formats are: –Book_code_title_year_author_numberOfPages –Recording_code_title_year_performer_format Borrower data will be write to a file in one of three formats: Plain text, HTML and XML.

74 UML class diagram

75 Interface LibraryCatalogLoader /** * This interface declares a method for obtaining a library catalog * from a file. */ public interface LibraryCatalogLoader { /** * Loads the information in the specified file into a library * catalog and returns the catalog. * filename the name of the file that contains the catalog data. a Catalog}. FileNotFoundException if the specified file does not exist. IOException if there is an error reading the * information in the specified file. DataFormatException if the file contains malformed data. */ Catalog loadCatalog(String filename) throws IOException, FileNotFoundException, DataFormatException; }

76 Class FileLibraryCatalogLoader import java.util.*; import java.io.*; /** * Creates a library catalog and loads it with data stored in a file. * Catalog CatalogItem Recording Book */ public class FileLibraryCatalogLoader implements LibraryCatalogLoader { /* Prefix of a line with book data */ private final static String BOOK_PREFIX = "Book"; /* Prefix of a line with recording data */ private final static String RECORDING_PREFIX = "Recording"; /* Delimiter */ private final static String DELIM = "_";

77 Class FileLibraryCatalogLoader /** * Loads the information in the specified file into a library catalog and returns the catalog. filename The name of a file that contains catalog information. a library catalog. FileNotFoundException if the specified file does not exist. IOException if there is an error reading the information in the specified file. DataFormatException if the file contains malformed data. */ public Catalog loadCatalog (String filename) throws IOException, FileNotFoundException, DataFormatException { Catalog catalog = new Catalog(); BufferedReader reader = new BufferedReader(new FileReader(filename)); String line = reader.readLine(); while (line != null) { CatalogItem item = null; if (line.startsWith(BOOK_PREFIX)) { item = readBook(line); } else if (line.startsWith(RECORDING_PREFIX)) { item = readRecording(line); } else { throw new DataFormatException(line); } catalog.addItem(item); line = reader.readLine(); } return catalog; }

78 Class FileLibraryCatalogLoader /** * Extracts the book data in the specified line and returns * a Book} object that encapsulates the book data. * line a string that contains book data. a Book object that encapsulates the * book data in the specified line. DataFormatException if the line contains errors. */ private Book readBook (String line) throws DataFormatException { StringTokenizer tokenizer = new StringTokenizer(line, DELIM); if (tokenizer.countTokens() != 6) { throw new DataFormatException(line); } else { try { String prefix = tokenizer.nextToken(); return new Book (tokenizer.nextToken(), tokenizer.nextToken(), Integer.parseInt(tokenizer.nextToken()), tokenizer.nextToken(), Integer.parseInt(tokenizer.nextToken())); } catch (NumberFormatException nfe) { throw new DataFormatException(line); } } }

79 Class FileLibraryCatalogLoader /** * Extracts the recording data in the specified line and returns * a Recording} object that encapsulates the book data. * line a string that contains recording data. a Recording object that encapsulates the * recording data in the specified line. DataFormatException if the line contains errors. */ private Recording readRecording (String line) throws DataFormatException { StringTokenizer tokenizer = new StringTokenizer(line, DELIM); if (tokenizer.countTokens() != 6) { throw new DataFormatException(line); } else { try { String prefix = tokenizer.nextToken(); return new Recording (tokenizer.nextToken(), tokenizer.nextToken(), Integer.parseInt( tokenizer.nextToken()), tokenizer.nextToken(), tokenizer.nextToken()); } catch (NumberFormatException nfe) { throw new DataFormatException(line); } } } }

80 Class DataFormatException /** * This exception is thrown when malformed data is detected while * a file being parsed. */ public class DataFormatException extends Exception { /** * Constructs a DataFormatException with no detail message. */ public DataFormatException() { } /** * Constructs a DataFormatException with the * specified detail message. * message the malformed data */ public DataFormatException(String message) { super(message); }

81 Writing Data to a File LibrarySystem.java

82 Complete Library System The following files implement this version of the library system: –Book.java –Recording.java –CatalogItem.java –Catalog.java –Borrower.java –BorrowedItems.java –BorrowerDatabase.java –BorrowersFormatter.java –PlainTextBorrowersFormatter.java –HTMLBorrowersFormatter.java –XMLBorrowersFormatter.java