public interface WritableComparable<T> extends Writable, Comparable<T>
Writable
which is also Comparable
.
WritableComparable
s can be compared to each other, typically
via Comparator
s. Any type which is to be used as a
key
in the Hadoop Map-Reduce framework should implement this
interface.
Example:
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)); } }
readFields, write
compareTo
Copyright © 2009 The Apache Software Foundation