WritableComparator (Apache Hadoop Main 3.1.1 API)

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 implementation 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

All Methods Static Methods Instance Methods Concrete 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
comparing, comparing, comparingDouble, comparingInt, comparingLong, equals, naturalOrder, nullsFirst, nullsLast, reversed, reverseOrder, thenComparing, thenComparing, thenComparing, thenComparingDouble, thenComparingInt, thenComparingLong

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

Class WritableComparator

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Comparator

Constructor Detail

WritableComparator

WritableComparator

WritableComparator

WritableComparator

Method Detail

get

get

setConf

getConf

define

getKeyClass

newKey

compare

compare

compare

compareBytes

hashBytes

hashBytes

readUnsignedShort

readInt

readFloat

readLong

readDouble

readVLong

readVInt