org.apache.hadoop.io

Class WritableComparator

java.lang.Object

org.apache.hadoop.io.WritableComparator

All Implemented Interfaces:

Comparator, Configurable, RawComparator

Direct Known Subclasses:

KeyFieldBasedComparator, RecordComparator

@InterfaceAudience.Public
@InterfaceStability.Stable
public class WritableComparator
extends Object
implements RawComparator, Configurable

A Comparator for WritableComparables.

This base implemenation uses the natural ordering. To define alternate orderings, override compare(WritableComparable,WritableComparable).

One may optimize compare-intensive operations by overriding compare(byte[],int,int,byte[],int,int). Static utility methods are provided to assist in optimized implementations of this method.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	WritableComparator()
protected	WritableComparator(Class<? extends WritableComparable> keyClass) Construct for a WritableComparable implementation.
protected	WritableComparator(Class<? extends WritableComparable> keyClass, boolean createInstances)
protected	WritableComparator(Class<? extends WritableComparable> keyClass, Configuration conf, boolean createInstances)

Method Summary

Methods

Modifier and Type	Method and Description
int	compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2) Optimization hook.
int	compare(Object a, Object b)
int	compare(WritableComparable a, WritableComparable b) Compare two WritableComparables.
static int	compareBytes(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2) Lexicographic order of binary data.
static void	define(Class c, WritableComparator comparator) Register an optimized comparator for a WritableComparable implementation.
static WritableComparator	get(Class<? extends WritableComparable> c) For backwards compatibility.
static WritableComparator	get(Class<? extends WritableComparable> c, Configuration conf) Get a comparator for a WritableComparable implementation.
Configuration	getConf() Return the configuration used by this object.
Class<? extends WritableComparable>	getKeyClass() Returns the WritableComparable implementation class.
static int	hashBytes(byte[] bytes, int length) Compute hash for binary data.
static int	hashBytes(byte[] bytes, int offset, int length) Compute hash for binary data.
WritableComparable	newKey() Construct a new WritableComparable instance.
static double	readDouble(byte[] bytes, int start) Parse a double from a byte array.
static float	readFloat(byte[] bytes, int start) Parse a float from a byte array.
static int	readInt(byte[] bytes, int start) Parse an integer from a byte array.
static long	readLong(byte[] bytes, int start) Parse a long from a byte array.
static int	readUnsignedShort(byte[] bytes, int start) Parse an unsigned short from a byte array.
static int	readVInt(byte[] bytes, int start) Reads a zero-compressed encoded integer from a byte array and returns it.
static long	readVLong(byte[] bytes, int start) Reads a zero-compressed encoded long from a byte array and returns it.
void	setConf(Configuration conf) Set the configuration to be used by this object.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.util.Comparator

equals

Constructor Detail

WritableComparator

protected WritableComparator()

WritableComparator

protected WritableComparator(Class<? extends WritableComparable> keyClass)

Construct for a WritableComparable implementation.

WritableComparator

protected WritableComparator(Class<? extends WritableComparable> keyClass,
                  boolean createInstances)

WritableComparator

protected WritableComparator(Class<? extends WritableComparable> keyClass,
                  Configuration conf,
                  boolean createInstances)

Method Detail

get

public static WritableComparator get(Class<? extends WritableComparable> c)

For backwards compatibility.

get

public static WritableComparator get(Class<? extends WritableComparable> c,
                     Configuration conf)

Get a comparator for a WritableComparable implementation.

setConf

public void setConf(Configuration conf)

Description copied from interface: Configurable

Set the configuration to be used by this object.

Specified by:

setConf in interface Configurable

getConf

public Configuration getConf()

Description copied from interface: Configurable

Return the configuration used by this object.

Specified by:

getConf in interface Configurable

define

public static void define(Class c,
          WritableComparator comparator)

Register an optimized comparator for a WritableComparable implementation. Comparators registered with this method must be thread-safe.

getKeyClass

public Class<? extends WritableComparable> getKeyClass()

Returns the WritableComparable implementation class.

newKey

public WritableComparable newKey()

Construct a new WritableComparable instance.

compare

public int compare(byte[] b1,
          int s1,
          int l1,
          byte[] b2,
          int s2,
          int l2)

Optimization hook. Override this to make SequenceFile.Sorter's scream.

The default implementation reads the data into two WritableComparables (using Writable.readFields(DataInput), then calls compare(WritableComparable,WritableComparable).

Specified by:

compare in interface RawComparator

Parameters:

b1 - The first byte array.

s1 - The position index in b1. The object under comparison's starting index.

l1 - The length of the object in b1.

b2 - The second byte array.

s2 - The position index in b2. The object under comparison's starting index.

l2 - The length of the object under comparison in b2.

Returns:

An integer result of the comparison.

compare

public int compare(WritableComparable a,
          WritableComparable b)

Compare two WritableComparables.

The default implementation uses the natural ordering, calling Comparable.compareTo(Object).

compare

public int compare(Object a,
          Object b)

Specified by:

compare in interface Comparator

compareBytes

public static int compareBytes(byte[] b1,
               int s1,
               int l1,
               byte[] b2,
               int s2,
               int l2)

Lexicographic order of binary data.

hashBytes

public static int hashBytes(byte[] bytes,
            int offset,
            int length)

Compute hash for binary data.

hashBytes

public static int hashBytes(byte[] bytes,
            int length)

Compute hash for binary data.

readUnsignedShort

public static int readUnsignedShort(byte[] bytes,
                    int start)

Parse an unsigned short from a byte array.

readInt

public static int readInt(byte[] bytes,
          int start)

Parse an integer from a byte array.

readFloat

public static float readFloat(byte[] bytes,
              int start)

Parse a float from a byte array.

readLong

public static long readLong(byte[] bytes,
            int start)

Parse a long from a byte array.

readDouble

public static double readDouble(byte[] bytes,
                int start)

Parse a double from a byte array.

readVLong

public static long readVLong(byte[] bytes,
             int start)
                      throws IOException

Reads a zero-compressed encoded long from a byte array and returns it.

Parameters:

bytes - byte array with decode long

start - starting index

Returns:

deserialized long

Throws:

IOException

readVInt

public static int readVInt(byte[] bytes,
           int start)
                    throws IOException

Reads a zero-compressed encoded integer from a byte array and returns it.

Parameters:

bytes - byte array with the encoded integer

start - start index

Returns:

deserialized integer

Throws:

IOException