org.apache.hadoop.hdfs.util
Class LightWeightHashSet<T>

java.lang.Object
  org.apache.hadoop.hdfs.util.LightWeightHashSet<T>

All Implemented Interfaces:

Iterable<T>, Collection<T>

Direct Known Subclasses:

LightWeightLinkedSet

public class LightWeightHashSet<T>
extends Object
implements Collection<T>

A low memory linked hash set implementation, which uses an array for storing the elements and linked lists for collision resolution. This class does not support null element. This class is not thread safe.

Field Summary

protected static float	DEFAULT_MAX_LOAD_FACTOR
protected static float	DEFAUT_MIN_LOAD_FACTOR
protected org.apache.hadoop.hdfs.util.LightWeightHashSet.LinkedElement<T>[]	entries An internal array of entries, which are the rows of the hash table.
protected static int	MINIMUM_CAPACITY
protected int	modification Modification version for fail-fast.
protected int	size The size of the set (not the entry array).

Constructor Summary

LightWeightHashSet()

LightWeightHashSet(int minCapacity)

LightWeightHashSet(int initCapacity, float maxLoadFactor, float minLoadFactor)

Method Summary

boolean	add(T element) Add given element to the hash table.
boolean	addAll(Collection<? extends T> toAdd) All all elements in the collection.
protected boolean	addElem(T element) Add given element to the hash table
void	clear() Clear the set.
boolean	contains(Object key) Check if the set contains given element
boolean	containsAll(Collection<?> c)
protected void	expandIfNecessary() Checks if we need to expand, and expands if necessary.
int	getCapacity() Return the current capacity (for testing).
protected T	getContainedElem(int index, T key, int hashCode) Check if the set contains given element at given index.
T	getElement(T key) Return the element in this set which is equal to the given key, if such an element exists.
protected int	getIndex(int hashCode) Get index in the internal table for a given hash.
boolean	isEmpty() Check if the set is empty.
Iterator<T>	iterator()
List<T>	pollAll() Remove all elements from the set and return them.
List<T>	pollN(int n) Remove and return n elements from the hashtable.
T[]	pollToArray(T[] array) Get array.length elements from the set, and put them into the array.
void	printDetails(PrintStream out) Print detailed information of this object.
boolean	remove(Object key) Remove the element corresponding to the key.
boolean	removeAll(Collection<?> c)
protected org.apache.hadoop.hdfs.util.LightWeightHashSet.LinkedElement<T>	removeElem(T key) Remove the element corresponding to the key, given key.hashCode() == index.
boolean	retainAll(Collection<?> c)
protected void	shrinkIfNecessary() Checks if we need to shrink, and shrinks if necessary.
int	size() Return the number of stored elements.
Object[]	toArray()
<U> U[]	toArray(U[] a)
String	toString()

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Collection

equals, hashCode

Field Detail

DEFAULT_MAX_LOAD_FACTOR

protected static final float DEFAULT_MAX_LOAD_FACTOR

See Also:

Constant Field Values

DEFAUT_MIN_LOAD_FACTOR

protected static final float DEFAUT_MIN_LOAD_FACTOR

See Also:

Constant Field Values

MINIMUM_CAPACITY

protected static final int MINIMUM_CAPACITY

See Also:

Constant Field Values

entries

protected org.apache.hadoop.hdfs.util.LightWeightHashSet.LinkedElement<T>[] entries

An internal array of entries, which are the rows of the hash table. The size must be a power of two.

size

protected int size

The size of the set (not the entry array).

modification

protected volatile int modification

Modification version for fail-fast.

See Also:

ConcurrentModificationException

Constructor Detail

LightWeightHashSet

public LightWeightHashSet(int initCapacity,
                          float maxLoadFactor,
                          float minLoadFactor)

Parameters:

initCapacity - Recommended size of the internal array.

maxLoadFactor - used to determine when to expand the internal array

minLoadFactor - used to determine when to shrink the internal array

LightWeightHashSet

public LightWeightHashSet()

LightWeightHashSet

public LightWeightHashSet(int minCapacity)

Method Detail

isEmpty

public boolean isEmpty()

Check if the set is empty.

Specified by:

isEmpty in interface Collection<T>

Returns:

true is set empty, false otherwise

getCapacity

public int getCapacity()

Return the current capacity (for testing).

size

public int size()

Return the number of stored elements.

Specified by:

size in interface Collection<T>

getIndex

protected int getIndex(int hashCode)

Get index in the internal table for a given hash.

contains

public boolean contains(Object key)

Check if the set contains given element

Specified by:

contains in interface Collection<T>

Returns:

true if element present, false otherwise.

getElement

public T getElement(T key)

Return the element in this set which is equal to the given key, if such an element exists. Otherwise returns null.

getContainedElem

protected T getContainedElem(int index,
                             T key,
                             int hashCode)

Check if the set contains given element at given index. If it does, return that element.

Returns:

the element, or null, if no element matches

addAll

public boolean addAll(Collection<? extends T> toAdd)

All all elements in the collection. Expand if necessary.

Specified by:

addAll in interface Collection<T>

Parameters:

toAdd - - elements to add.

Returns:

true if the set has changed, false otherwise

add

public boolean add(T element)

Add given element to the hash table. Expand table if necessary.

Specified by:

add in interface Collection<T>

Returns:

true if the element was not present in the table, false otherwise

addElem

protected boolean addElem(T element)

Add given element to the hash table

Returns:

true if the element was not present in the table, false otherwise

remove

public boolean remove(Object key)

Remove the element corresponding to the key.

Specified by:

remove in interface Collection<T>

Returns:

If such element exists, return true. Otherwise, return false.

removeElem

protected org.apache.hadoop.hdfs.util.LightWeightHashSet.LinkedElement<T> removeElem(T key)

Remove the element corresponding to the key, given key.hashCode() == index.

Returns:

If such element exists, return true. Otherwise, return false.

pollN

public List<T> pollN(int n)

Remove and return n elements from the hashtable. The order in which entries are removed is unspecified, and and may not correspond to the order in which they were inserted.

Returns:

first element

pollAll

public List<T> pollAll()

Remove all elements from the set and return them. Clear the entries.

pollToArray

public T[] pollToArray(T[] array)

Get array.length elements from the set, and put them into the array.

shrinkIfNecessary

protected void shrinkIfNecessary()

Checks if we need to shrink, and shrinks if necessary.

expandIfNecessary

protected void expandIfNecessary()

Checks if we need to expand, and expands if necessary.

iterator

public Iterator<T> iterator()

Specified by:

iterator in interface Iterable<T>

Specified by:

iterator in interface Collection<T>

toString

public String toString()

Overrides:

toString in class Object

printDetails

public void printDetails(PrintStream out)

Print detailed information of this object.

clear

public void clear()

Clear the set. Resize it to the original capacity.

Specified by:

clear in interface Collection<T>

toArray

public Object[] toArray()

Specified by:

toArray in interface Collection<T>

toArray

public <U> U[] toArray(U[] a)

Specified by:

toArray in interface Collection<T>

containsAll

public boolean containsAll(Collection<?> c)

Specified by:

containsAll in interface Collection<T>

removeAll

public boolean removeAll(Collection<?> c)

Specified by:

removeAll in interface Collection<T>

retainAll

public boolean retainAll(Collection<?> c)

Specified by:

retainAll in interface Collection<T>