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From "Trevor Robinson (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-5020) Compile failure with JDK8
Date Thu, 21 Feb 2013 21:14:12 GMT
Trevor Robinson created MAPREDUCE-5020:
------------------------------------------

             Summary: Compile failure with JDK8
                 Key: MAPREDUCE-5020
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5020
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: client
    Affects Versions: 2.0.3-alpha
         Environment: java version "1.8.0-ea"
Java(TM) SE Runtime Environment (build 1.8.0-ea-b36e)
Java HotSpot(TM) Client VM (build 25.0-b04, mixed mode)
            Reporter: Trevor Robinson


Compiling `org/apache/hadoop/mapreduce/lib/partition/InputSampler.java` fails with the Java
8 preview compiler due to its stricter enforcement of JLS 15.12.2.6 (for [Java 5|http://docs.oracle.com/javase/specs/jls/se5.0/html/expressions.html#15.12.2.6]
or [Java 7|http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.12.2.6]), which
demands that methods applicable via unchecked conversion have their return type erased:

{noformat}
[ERROR] hadoop-common/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/lib/partition/InputSampler.java:[320,35]
error: incompatible types: Object[] cannot be converted to K[]
{noformat}

{code}
  @SuppressWarnings("unchecked") // getInputFormat, getOutputKeyComparator
  public static <K,V> void writePartitionFile(Job job, Sampler<K,V> sampler) 
      throws IOException, ClassNotFoundException, InterruptedException {
    Configuration conf = job.getConfiguration();
    final InputFormat inf = 
        ReflectionUtils.newInstance(job.getInputFormatClass(), conf);
    int numPartitions = job.getNumReduceTasks();
    K[] samples = sampler.getSample(inf, job); // returns Object[] according to JLS
{code}

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