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

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## org.apache.hadoop.mapreduce
Class ReduceContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT>

    java.lang.Object
      org.apache.hadoop.mapreduce.JobContext
          org.apache.hadoop.mapreduce.TaskAttemptContext
              org.apache.hadoop.mapreduce.TaskInputOutputContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT>
                  org.apache.hadoop.mapreduce.ReduceContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT>

Type Parameters:
  `KEYIN` - the class of the input keys
  `VALUEIN` - the class of the input values
  `KEYOUT` - the class of the output keys
  `VALUEOUT` - the class of the output values

All Implemented Interfaces:
  Progressable

Direct Known Subclasses:
  Reducer.Context

    public class ReduceContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT>

extends TaskInputOutputContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT>

The context passed to the `Reducer`.

Nested Class Summary
`protected class` | `ReduceContext.ValueIterable`
`protected class` | `ReduceContext.ValueIterator`

Field Summary
`protected Progressable` | `reporter`

Fields inherited from class org.apache.hadoop.mapreduce.JobContext
`CACHE_ARCHIVES_VISIBILITIES, CACHE_FILE_VISIBILITIES, COMBINE_CLASS_ATTR, conf, credentials, INPUT_FORMAT_CLASS_ATTR, JOB_ACL_MODIFY_JOB, JOB_ACL_VIEW_JOB, JOB_CANCEL_DELEGATION_TOKEN, JOB_NAMENODES, MAP_CLASS_ATTR, OUTPUT_FORMAT_CLASS_ATTR, PARTITIONER_CLASS_ATTR, REDUCE_CLASS_ATTR, ugi, USER_LOG_RETAIN_HOURS`

Constructor Summary
`ReduceContext(Configuration conf, TaskAttemptID taskid, RawKeyValueIterator input, Counter inputKeyCounter, Counter inputValueCounter, RecordWriter<KEYOUT,VALUEOUT> output, OutputCommitter committer, StatusReporter reporter, RawComparator<KEYIN> comparator, Class<KEYIN> keyClass, Class<VALUEIN> valueClass)`

Method Summary
`KEYIN` | `getCurrentKey()` Get the current key.
`VALUEIN` | `getCurrentValue()` Get the current value.
`Iterable<VALUEIN>` | `getValues()` Iterate through the values for the current key, reusing the same value object, which is stored in the context.
`boolean` | `nextKey()` Start processing next unique key.
`boolean` | `nextKeyValue()` Advance to the next key/value pair.

Methods inherited from class org.apache.hadoop.mapreduce.TaskInputOutputContext
`getCounter, getCounter, getOutputCommitter, getProgress, progress, setStatus, write`

Methods inherited from class org.apache.hadoop.mapreduce.TaskAttemptContext
`getStatus, getTaskAttemptID`

Methods inherited from class org.apache.hadoop.mapreduce.JobContext
`getCombinerClass, getConfiguration, getCredentials, getGroupingComparator, getInputFormatClass, getJar, getJobID, getJobName, getMapOutputKeyClass, getMapOutputValueClass, getMapperClass, getNumReduceTasks, getOutputFormatClass, getOutputKeyClass, getOutputValueClass, getPartitionerClass, getReducerClass, getSortComparator, getWorkingDirectory`

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

Field Detail

### reporter

    protected Progressable reporter

Constructor Detail

### ReduceContext

    public ReduceContext(Configuration conf,
                         TaskAttemptID taskid,
                         RawKeyValueIterator input,
                         Counter inputKeyCounter,
                         Counter inputValueCounter,
                         RecordWriter<KEYOUT,VALUEOUT> output,
                         OutputCommitter committer,
                         StatusReporter reporter,
                         RawComparator<KEYIN> comparator,
                         Class<KEYIN> keyClass,
                         Class<VALUEIN> valueClass)
                  throws InterruptedException,
                         IOException

Throws:
  `InterruptedException`
  `IOException`

Method Detail

### nextKey

    public boolean nextKey()
                    throws IOException,
                           InterruptedException

  Start processing next unique key.

  Throws:
    `IOException`
    `InterruptedException`

### nextKeyValue

    public boolean nextKeyValue()
                         throws IOException,
                                InterruptedException

  Advance to the next key/value pair.

  Specified by:
    `nextKeyValue` in class `TaskInputOutputContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT>`
  Returns:
    the key object that was read into, or null if no more
  Throws:
    `IOException`
    `InterruptedException`

### getCurrentKey

    public KEYIN getCurrentKey()

  Description copied from class: `TaskInputOutputContext`
  Get the current key.

  Specified by:
    `getCurrentKey` in class `TaskInputOutputContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT>`
  Returns:
    the current key object or null if there isn't one

### getCurrentValue

    public VALUEIN getCurrentValue()

  Description copied from class: `TaskInputOutputContext`
  Get the current value.

  Specified by:
    `getCurrentValue` in class `TaskInputOutputContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT>`
  Returns:
    the value object that was read into

### getValues

    public Iterable<VALUEIN> getValues()
                                throws IOException,
                                       InterruptedException

  Iterate through the values for the current key, reusing the same value object, which is stored in the context.

  Returns:
    the series of values associated with the current key. All of the objects returned directly and indirectly from this method are reused.
  Throws:
    `IOException`
    `InterruptedException`

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