[MAPREDUCE-5020] Compile failure with JDK8

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.0.3-alpha, 2.1.0-beta
• Fix Version/s: 2.1.1-beta
• Component/s: client
• Labels: build-failure jdk8

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)

• Target Version/s: 2.1.1-beta
• Assignee: Trevor Robinson
• Reporter: Trevor Robinson
• Created: 21/Feb/13 21:12
• Updated: 03/Sep/14 23:31
• Resolved: 10/Sep/13 19:10

Description

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 or Java 7), which demands that methods applicable via unchecked conversion have their return type erased:

[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[]

  @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