[Chapter 18] Checksum

Synopsis

Interface Name:

java.util.zip.Checksum

Super-interface:

None

Immediate Sub-interfaces:

None

Implemented By:

java.util.zip.Adler32, java.util.zip.CRC32

Availability:

New as of JDK 1.1

The Checksum interface defines the methods that are needed to compute a checksum value for a stream of data. The checksum value can be used for error checking purposes. Note, however, that the checksum value must fit into a long value, so this interface is not suitable for cryptographic checksum algorithms.

The Adler32 and CRC32 classes implement the Checksum interface, using the Adler-32 and CRC-32 algorithms, respectively. The CheckedInputStream and CheckedOutputStream classes provide a higher-level mechanism for computing checksums on data streams.

Class Summary

public abstract interface java.util.zip.Checksum {
  // Methods
  public abstract long getValue();
  public abstract void reset();
  public abstract void update(int b);
  public abstract void update(byte[] b, int off, int len);
}

Methods

getValue

public abstract long getValue()

Returns

The current checksum value.

Description

This method returns the current value of this checksum.

reset

public abstract void reset()

Description: This method resets the checksum to its initial value, making it appear as though it has not been updated by any data.

update

public abstract void update(int b)

Parameters

b: The value to be added to the data stream for the checksum calculation.

Description

This method adds the specified value to the data stream and updates the checksum value. The method uses only the lowest eight bits of the given int.

public abstract void update(byte[] b, int off, int len)

Parameters

b

An array of bytes to be added to the data stream for the checksum calculation.

off

An offset into the byte array.

len

The number of bytes to use.

Description

This method adds len bytes from the specified array, starting at off, to the data stream and updates the checksum value.


CheckedOutputStream		CRC32