Package org.apache.hadoop.util

Class IdentityHashStore<K,V>

java.lang.Object

org.apache.hadoop.util.IdentityHashStore<K,V>

Type Parameters:

K - The key type to use.

V - THe value type to use.

@Private
@Evolving
public final class IdentityHashStore<K,V>
extends java.lang.Object

The IdentityHashStore stores (key, value) mappings in an array. It is similar to java.util.HashTable, but much more lightweight. Neither inserting nor removing an element ever leads to any garbage getting created (assuming the array doesn't need to be enlarged). Unlike HashTable, it compares keys using System.identityHashCode(Object) and the identity operator. This is useful for types like ByteBuffer which have expensive hashCode and equals operators. We use linear probing to resolve collisions. This avoids the need for the overhead of linked list data structures. It also means that it is expensive to attempt to remove an element that isn't there, since we have to look at the entire array to be sure that it doesn't exist.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	IdentityHashStore.Visitor<K,V>

Constructor Summary

Constructors

Constructor	Description
IdentityHashStore(int capacity)

Method Summary

Modifier and Type	Method	Description
int	capacity()
V	get(K k)	Retrieve a value associated with a given key.
boolean	isEmpty()
int	numElements()
void	put(K k, V v)	Add a new (key, value) mapping.
V	remove(K k)	Retrieve a value associated with a given key, and delete the relevant entry.
void	visitAll(IdentityHashStore.Visitor<K,V> visitor)	Visit all key, value pairs in the IdentityHashStore.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

IdentityHashStore

public IdentityHashStore(int capacity)

Method Detail

put

public void put(K k,
                V v)

Add a new (key, value) mapping. Inserting a new (key, value) never overwrites a previous one. In other words, you can insert the same key multiple times and it will lead to multiple entries.

Parameters:

k - Generics Type k.

v - Generics Type v.

get

public V get(K k)

Retrieve a value associated with a given key.

Parameters:

k - Generics Type k.

Returns:

Generics Type V.

remove

public V remove(K k)

Retrieve a value associated with a given key, and delete the relevant entry.

Parameters:

k - Generics Type k.

Returns:

Generics Type V.

isEmpty

public boolean isEmpty()

numElements

public int numElements()

capacity

public int capacity()

visitAll

public void visitAll(IdentityHashStore.Visitor<K,V> visitor)

Visit all key, value pairs in the IdentityHashStore.

Parameters:

visitor - visitor.