Title Description Participants Textbook

Transcription

1 Podcast Ch23c Title: Binary Files Description: Overview of binary files; DataInputStream; DataOutputStream; Program 23.1; file compression Participants: Barry Kurtz (instructor); John Helfert and Tobie Williams (students) Textbook: Data Structures for Java; William H. Ford and William R. Topp

2 Binary Files File types are text files and binary files. Java deals with files by creating a byte stream that connects the file and the application. Binary files can be handled with DataInputStream and DataOutputStream classes.

3 Binary Files (continued) A data input stream lets an application read primitive Java data types from an underlying input stream in a machineindependent way. A data output stream lets an application write primitive Java data types to an output stream in a portable way. An application can then use a data input stream to read the data back in.

4 Binary Files (continued) classes DataInputStream and DataOutputStream Constructors java.io DataInputStream(InputStream in) Creates a DataInputStream that uses the specified underlying InputStream. DataOutputStream(OutputStream out) Creates a new data output stream to write data to the specified underlying output stream.

5 Binary Files (continued) classes DataInputStream and DataOutputStream Methods java.io void close() throws IOException Closes a stream and releases any system resources associated with the stream. int void read(byte[] b) throws IOException Reads some number of bytes from the input stream and stores them into the byte array b. The return value is the number of bytes actually read or -1 if there is no more data because the end of the stream has been reached. write(byte[] b, int off, int len) throws IOException Writes len bytes from the specified byte array starting at array index off to the underlying output stream.

6 Binary Files (continued) classes DataInputStream and DataOutputStream int void long void Methods (continued) java.io readint() throws IOException Reads four input bytes and returns an int value in a machineindependent fashion. This method is suitable for reading bytes written by the writeint() method. Throws EOFException if this file reaches the end before reading four bytes. writeint(int v) throws IOException Writes an int to the underlying output stream as four bytes. readlong() throws IOException Reads eight input bytes and returns a long value in a machineindependent fashion. This method is suitable for reading bytes written by the writelong() method. Throws EOFException if this file reaches the end before reading eight bytes. writelong(long v) throws IOException Writes a long to the underlying output stream as eight bytes.

7 Binary Files (continued) classes DataInputStream and DataOutputStream short void Methods (continued) java.io readshort() throws IOException Reads two input bytes and returns a short value in a machineindependent fashion. This method is suitable for reading bytes written by the writeshort() method. Throws EOFException if this file reaches the end before reading two bytes. writeshort(int v) throws IOException Writes a short to the underlying output stream as two bytes. int available() throws IOException Returns the number of bytes that can be read from this input stream without blocking.

8 Program 23.1 (Run) int: 100 short: 1500 long: byte array:

9 import java.io.*; Program 23.1 public class Program23_1 { public static void main(string[] args) throws IOException { int intval = 100; short shortval = 1500; long longval = L; byte[] buf = {3, 5, 2, 7, 15, 100, 127, 55}; // create a DataOutputStream that writes to // the file "data.dat" in the local directory DataOutputStream fout = null; // use to input data from "data.dat" DataInputStream fin = null;

10 Program 23.1 (continued) try { fout = new DataOutputStream( new FileOutputStream("data.dat")); } catch (FileNotFoundException fnfe) { System.err.println("Cannot create \"data.dat\""); System.exit(1); } // write each variable and the array to f fout.writeint(intval); fout.writeshort(shortval); fout.writelong(longval); fout.write(buf, 0, buf.length);

11 Program 23.1 (continued) // close the stream and open it // as a DataInputStream fout.close(); try { fin = new DataInputStream(new FileInputStream( "data.dat")); } catch (FileNotFoundException fnfe) { System.err.println("Failure to open " + "\"data.dat\""); System.exit(1); } // input the int, short, and long from the file System.out.println("int: " + fin.readint()); System.out.println("short: " + fin.readshort()); System.out.println("long: " + fin.readlong());

12 Program 23.1 (concluded) } } // input the byte array that was written // to the file; the number of bytes in the // array is the number of bytes remaining // unread in the file byte[] b = new byte[fin.available()]; System.out.print("byte array: "); // input the array fin.read(b); // output the bytes for (int i=0; i < b.length; i++) System.out.print(b[i] + " "); System.out.println(); // close the stream fin.close();

13 File Compression Lossless compression loses no data and is used for data backup.

14 File Compression (continued) Lossy compression is used for applications like sound and video compression and causes minor loss of data.

15 File Compression (continued) The compression ratio is the ratio of the number of bits in the original data to the number of bits in the compressed image. For instance, if a data file contains 500,000 bytes and the compressed data contains 100,000 bytes, the compression ratio is 5:1