WritableComparator (Apache Hadoop Main 0.23.11 API)

java.lang.Object
- org.apache.hadoop.io.WritableComparator

All Implemented Interfaces:

Comparator, RawComparator

Direct Known Subclasses:

KeyFieldBasedComparator, RecordComparator
```
@InterfaceAudience.Public
@InterfaceStability.Stable
public class WritableComparator
extends Object
implements RawComparator
```
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)`

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)` Get a comparator for a `WritableComparable` implementation.
`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.

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)
```
- Method Detail
  - get
```
public static WritableComparator get(Class<? extends WritableComparable> c)
```
    Get a comparator for a WritableComparable implementation.
  - 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

Method Detail

get

define

getKeyClass

newKey

compare

compare

compare

compareBytes

hashBytes

hashBytes

readUnsignedShort

readInt

readFloat

readLong

readDouble

readVLong

readVInt