edu.umd.cloud9.io
Class HashMapWritable<K extends Writable,V extends Writable>

java.lang.Object
  java.util.AbstractMap<K,V>
      java.util.HashMap<K,V>
          edu.umd.cloud9.io.HashMapWritable<K,V>

Type Parameters:

K - type of the key

V - type of the value

All Implemented Interfaces:

Serializable, Cloneable, Map<K,V>, Writable

public class HashMapWritable<K extends Writable,V extends Writable>
extends HashMap<K,V>
implements Writable

Writable extension of a Java HashMap. This generic class supports the use of any type as either key or value. For a feature vector, use either VectorInt or VectorFloat for a more efficient implementation.

There are a number of key differences between this class and Hadoop's MapWritable:

• MapWritable is more flexible in that it supports heterogeneous elements. In this class, all keys must be of the same type and all values must be of the same type. This assumption allows a simpler serialization protocol and thus is more efficient. Run main in this class for a simple efficiency test.
• This class is generic, whereas MapWritable isn't.

For a comparison of efficiency, see BenchmarkHashMapWritable.

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class java.util.AbstractMap

AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>

Constructor Summary

HashMapWritable()
Creates a HashMapWritable object.

HashMapWritable(HashMap<K,V> map)
Creates a HashMapWritable object from a regular HashMap.

Method Summary

void	readFields(DataInput in) Deserializes the array.
void	write(DataOutput out) Serializes this array.

Methods inherited from class java.util.HashMap

clear, clone, containsKey, containsValue, entrySet, get, isEmpty, keySet, put, putAll, remove, size, values

Methods inherited from class java.util.AbstractMap

equals, hashCode, toString

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map

equals, hashCode

Constructor Detail

HashMapWritable

public HashMapWritable()

Creates a HashMapWritable object.

HashMapWritable

public HashMapWritable(HashMap<K,V> map)

Creates a HashMapWritable object from a regular HashMap.

Method Detail

readFields

public void readFields(DataInput in)
                throws IOException

Deserializes the array.

Specified by:

readFields in interface Writable

Parameters:

in - source for raw byte representation

Throws:

IOException

write

public void write(DataOutput out)
           throws IOException

Serializes this array.

Specified by:

write in interface Writable

Parameters:

out - where to write the raw byte representation

Throws:

IOException