AbstractMapWritable (Hadoop 1.2.1 API)
Date: 2013-07-22

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## org.apache.hadoop.io
Class AbstractMapWritable

    java.lang.Object
      org.apache.hadoop.io.AbstractMapWritable

All Implemented Interfaces:
  Configurable, Writable

Direct Known Subclasses:
  MapWritable, SortedMapWritable

    public abstract class AbstractMapWritable

extends Object
implements Writable, Configurable

Abstract base class for MapWritable and SortedMapWritable Unlike org.apache.nutch.crawl.MapWritable, this class allows creation of MapWritable<Writable, MapWritable> so the CLASS_TO_ID and ID_TO_CLASS maps travel with the class instead of being static. Class ids range from 1 to 127 so there can be at most 127 distinct classes in any specific map instance.

Constructor Summary
`protected` | `AbstractMapWritable()` constructor.

Method Summary
`protected void` | `addToMap(Class clazz)` Add a Class to the maps if it is not already present.
`protected void` | `copy(Writable other)` Used by child copy constructors.
`protected Class` | `getClass(byte id)`
`Configuration` | `getConf()` Return the configuration used by this object.
`protected byte` | `getId(Class clazz)`
`void` | `readFields(DataInput in)` Deserialize the fields of this object from `in`.
`void` | `setConf(Configuration conf)` Set the configuration to be used by this object.
`void` | `write(DataOutput out)` Serialize the fields of this object to `out`.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### AbstractMapWritable

    protected AbstractMapWritable()

  constructor.

Method Detail

### addToMap

    protected void addToMap(Class clazz)

  Add a Class to the maps if it is not already present.

### getClass

    protected Class getClass(byte id)

  Returns:
    the Class class for the specified id

### getId

    protected byte getId(Class clazz)

  Returns:
    the id for the specified Class

### copy

    protected void copy(Writable other)

  Used by child copy constructors.

### getConf

    public Configuration getConf()

  Description copied from interface: `Configurable`
  Return the configuration used by this object.

  Specified by:
    `getConf` in interface `Configurable`
  Returns:
    the conf

### 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`
  Parameters:
    `conf` - the conf to set

### write

    public void write(DataOutput out)
               throws IOException

  Serialize the fields of this object to `out`.

  Specified by:
    `write` in interface `Writable`
  Parameters:
    `out` - `DataOuput` to serialize this object into.
  Throws:
    `IOException`

### readFields

    public void readFields(DataInput in)
                    throws IOException

  Deserialize the fields of this object from `in`.

  For efficiency, implementations should attempt to re-use storage in the existing object where possible.

  Specified by:
    `readFields` in interface `Writable`
  Parameters:
    `in` - `DataInput` to deseriablize this object from.
  Throws:
    `IOException`

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