Subclassing InputStream

Immediate subclasses of InputStream must provide an implementation of the abstract read( ) method. They may also override some of the nonabstract methods. For example, the default markSupported( ) method returns false, mark( ) does nothing, and reset( ) tHRows an IOException. Any class that allows marking and resetting must override these three methods. Subclasses should also override available( ) to return something other than 0. Furthermore, they may override skip( ) and the other two read( ) methods to provide more efficient implementations.

Example 3-2 is a simple class called RandomInputStream that "reads" random bytes of data. This provides a useful source of unlimited data you can use in testing. A java.util.Random object provides the data.

Example 3-2. The RandomInputStream class

package com.elharo.io;
import java.util.*;
import java.io.*;
public class RandomInputStream extends InputStream {
 private Random generator = new Random( );
 private boolean closed = false;
 public int read( ) throws IOException {
 checkOpen( );
 int result = generator.nextInt( ) % 256;
 if (result < 0) result = -result;
 return result;
 }
 public int read(byte[] data, int offset, int length) throws IOException {
 checkOpen( );
 byte[] temp = new byte[length];
 generator.nextBytes(temp);
 System.arraycopy(temp, 0, data, offset, length);
 return length;
 }
 public int read(byte[] data) throws IOException {
 checkOpen( );
 generator.nextBytes(data);
 return data.length;
 }
 public long skip(long bytesToSkip) throws IOException {
 checkOpen( );
 // It's all random so skipping has no effect.
 return bytesToSkip;
 }
 public void close( ) {
 this.closed = true;
 }
 private void checkOpen( ) throws IOException {
 if (closed) throw new IOException("Input stream closed");
 }
 public int available( ) {
 // Limited only by available memory and the size of an array.
 return Integer.MAX_VALUE;
 }
}

The no-argument read( ) method returns a random int in the range of an unsigned byte (0 to 255). The other two read( ) methods fill a specified part of an array with random bytes. They return the number of bytes read (in this case the number of bytes created).