Java IO.pdf - Nguyen Dang Binh

}
}
public long getValue() {
return checksum;
}
public void reset() {
checksum = 0;
}
Java I/O
The java.util.zip package provides two concrete implementations of the Checksum
interface, CRC32 and Adler32. Both produce 32-bit checksums. The Adler-32 algorithm is not
quite as reliable as CRC-32 but can be computed much faster. Both of these classes have a
single no-argument constructor:
public CRC32()
public Adler32()
They share the same five methods, four implementing the methods of the Checksum interface,
plus one additional update() method that reads an entire byte array:
public void update(int b)
public native void update(byte[] data, int offset, int length)
public void update(byte[] data)
public void reset()
public long getValue()
Example 9.13, FileSummer, is a simple program that calculates and prints a CRC-32
checksum for any file. However, it's structured such that the static getCRC32() method can
calculate a CRC-32 checksum for any stream.
Example 9.13. FileSummer
import java.io.*;
import java.util.zip.*;
public class FileSummer {
public static void main(String[] args) {
}
for (int i = 0; i < args.length; i++) {
try {
FileInputStream fin = new FileInputStream(args[i]);
System.out.println(args[i] + ":\t" + getCRC32(fin));
fin.close();
}
catch (IOException e) {System.err.println(e);}
}
public static long getCRC32(InputStream in) throws IOException {
Checksum cs = new CRC32();
// It would be more efficient to read chunks of data
// at a time, but this is simpler and easier to understand.
174