com.aliyun.odps.io

接口 WritableComparable<T>

所有超级接口:

Comparable<T>, Writable

所有已知子接口:

InputBlobWritable, OutputBlobWritable

所有已知实现类:

BooleanWritable, BytesWritable, DatetimeWritable, DoubleWritable, IntWritable, LongWritable, NullWritable, Text, Tuple

public interface WritableComparable<T>
extends Writable, Comparable<T>

WritableComparable 接口同时继承了 Writable 和 Comparable.

WritableComparables 对象之间可以进行比较，Mapper 输出的 Key 都需要实现此接口用于排序.

代码示例:

 public class MyWritableComparable implements WritableComparable {
   // Some data
   private int counter;
   private long timestamp;

   public void write(DataOutput out) throws IOException {
     out.writeInt(counter);
     out.writeLong(timestamp);
   }

   public void readFields(DataInput in) throws IOException {
     counter = in.readInt();
     timestamp = in.readLong();
   }

   public int compareTo(MyWritableComparable w) {
     int thisValue = this.value;
     int thatValue = ((IntWritable) o).value;
     return (thisValue < thatValue ? -1 : (thisValue == thatValue ? 0 : 1));
   }
 }
 

方法概要

从接口继承的方法 com.aliyun.odps.io.Writable

readFields, write

从接口继承的方法 java.lang.Comparable

compareTo