• FilterInputStream
  • Parent of all filtered input streams
  • By default, performs a simple pass-thru
• To Filter:
  • Use the protected InputStream in
  • Override:

                  int read()
    
                  int read(byte[] b, int off, int len)
    
    	                       

• FilterOutputStream
  • Parent of all filtered output streams
  • By default, performs a simple pass-thru
• To Filter:
  • Use the protected OutputStream out
  • Override:

                  void write(byte[] b, int off, int len
    
                  void write(byte[] b)
    
    	                       

A Seven-Bit Input Stream

javaexamples/io/SevenBitInputStream.java

package io;

import java.io.*;


/**
 *  For stripping off the high bit of a byte
 *
 *  @version 1.0
 *  @author  Prof. David Bernstein, James Madison University
 */
public class SevenBitInputStream extends FilterInputStream
{
    /**
     * Explicit Value Constructor
     *
     * @param is   The underlying InputStream to filter
     */
    public SevenBitInputStream(InputStream is)
    {
        super(is);
    }


    /**
     * Reads the next byte of data from this input stream. 
     * The value byte is returned as an int in the range 0 to 127.
     *
     * @return The value of the byte (as an int)
     */
    public int read() throws IOException
    {
        int   i;

        i = in.read();     // in is a variable FilterInputStream
        return (i & 127);  // Bitwise AND
    }



    /**
     * Reads up to len bytes of data into an array of bytes. 
     *
     * @param b    The byte array into which the data are read
     * @param off  The start offset
     * @param len  The (maximum) number of bytes read
     * @return     The total number of bytes read
     */
    public int read(byte[] b, int off, int len) throws IOException
    {
        int    i, n;


        n = in.read(b, off, len);
        for (i=0; i < n; i++) b[i] = (byte)(b[i] & 127);

        return n;
    }

}