[Chapter 18] CRC32

#

| Chapter 18 The java.util.zip Package |

# CRC32

## Name

CRC32

## Synopsis

Class Name:

  `java.util.zip.CRC32`

Superclass:

  `java.lang.Object`

Immediate Subclasses:

  None

Interfaces Implemented:

  `java.util.zip.Checksum`

Availability:

  New as of JDK 1.1

## Description

The `CRC32` class implements the `Checksum` interface using the CRC-32 algorithm. This algorithm is significantly slower than Adler-32 and only slightly more reliable.

## Class Summary

    public class java.util.zip.CRC32 extends java.lang.Object
                 implements java.util.zip.Checksum {
      // Constructors
      public CRC32();

      // Instance Methods
      public long getValue();
      public void reset();
      public void update(int b);
      public void update(byte[] b);
      public native void update(byte[] b, int off, int len);
    }

## Constructors

### CRC32

#### public CRC32()

Description

  This constructor creates an `CRC32` object.

## Instance Methods

### getValue

#### public long getValue()

Returns

  The current checksum value.

Implements

  `Checksum.getValue()`

Description

  This method returns the current value of this checksum.

### reset

#### public void reset()

Implements

  `Checksum.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 void update(int b)

Parameters

  `b`

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

Implements

  `Checksum.update(int)`

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 void update(byte[] b)

Parameters

  `b`

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

Description

  This method adds the bytes from the specified array to the data stream and updates the checksum value.

#### public native 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.

Implements

  `Checksum.update(byte[], int, int)`

Description

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

## Inherited Methods

Method | Inherited From | Method | Inherited From
--- | --- | --- | ---
`clone()` | `Object` | `equals(Object)` | `Object`
`finalize()` | `Object` | `getClass()` | `Object`
`hashCode()` | `Object` | `notify()` | `Object`
`notifyAll()` | `Object` | `toString()` | `Object`
`wait()` | `Object` | `wait(long)` | `Object`
`wait(long, int)` | `Object` |  |

## See Also

`Adler32`, `Checksum`

Checksum |  | DataFormatException