Reading a Byte Stream in Java

Byte streams are used for processing files that do not contain human-readable text.

A .class file is meant for processing by the JVM, hence you must use byte streams to process the .class file.

The classes InputStream and OutputStream form the base of the hierarchies for byte streams. You perform file I/O, so open the given file as a FileInputStream.

In case you need to speed up the program when you read large number of bytes, you can use a buffered output stream.

BufferedInputStream bis = new BufferedInputStream(new FileInputStream(fileName));

you can use output streams to write sequence of bytes to a data file. You can use FileOutputStream and BufferedOutputStream.

DataStreamExample.java

package com.appfworks.io;

/**
 * Created by suresh on 31/10/15.
 */
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
// A simple class to illustrate data streams; write constants 0 and 1 in different data type values
// into a file and read the results back and print them
class DataStreamExample {
    public static void main(String []args) {
        // write some data into a data file with hard-coded name "temp.data"
        try (DataOutputStream dos =
                     new DataOutputStream(new FileOutputStream("temp.data"))) {
            // write values 1 to 10 as byte, short, int, long, float and double
            // omitting boolean type because an int value cannot
            // be converted to boolean
            for(int i = 0; i < 10; i++) {
                dos.writeByte(i);
                dos.writeShort(i);
                dos.writeInt(i);
                dos.writeLong(i);
                dos.writeFloat(i);
                dos.writeDouble(i);
            }
        } catch(FileNotFoundException fnfe) {
            System.err.println("cannot create a file with the given file name ");
            System.exit(-1); // don't proceed – exit the program
        } catch(IOException ioe) {
            System.err.println("an I/O error occurred while processing the file");
            System.exit(-1); // don't proceed – exit the program
        }
        // the DataOutputStream will auto-close, so don't have to worry about it
        // now, read the written data and print it to console
        try (DataInputStream dis = new DataInputStream(new FileInputStream("temp.data"))) {
            // the order of values to read is byte, short, int, long, float and
            // double
            // since we've written from 0 to 0, the for loop has to run 10 times
            for(int i = 0; i < 10; i++) {
                // %d is for printing byte, short, int or long
                // %f, %g, or %e is for printing float or double
                // %n is for printing newline
                System.out.printf("%d %d %d %d %g %g %n",
                        dis.readByte(),
                        dis.readShort(),
                        dis.readInt(),
                        dis.readLong(),
                        dis.readFloat(),
                        dis.readDouble());
            }
        } catch(FileNotFoundException fnfe) {
            System.err.println("cannot create a file with the given file name ");
        } catch(IOException ioe) {
            System.err.println("an I/O error occurred while processing the file");
        }   // the DataOutputStream will auto-close, so don't have to worry about it
    }
}