de.ipcon.tools

Class IndexedHashSet<E>

java.lang.Object

de.ipcon.tools.IndexedHashSet<E>

All Implemented Interfaces:

java.io.Externalizable, java.io.Serializable, java.lang.Iterable<E>, java.util.Collection<E>, java.util.List<E>, java.util.RandomAccess, java.util.Set<E>

public class IndexedHashSet<E>
extends java.lang.Object
implements java.util.Set<E>, java.util.List<E>, java.util.RandomAccess, java.io.Externalizable

A drop-in replacement for `HashSet` providing constant-time `contains()` operations. This comes with a slight performance penalty on `add()` and a linear penalty on `remove(index)`.

Additionally, this class offers:

• `indexOf()` to get the index of an element.
• An `iterator()` that preserves insertion order.

During construction, you can specify:

• `nullValuesAllowed`: Whether `null` elements are permitted. Defaults to `true`.
`referenceEquality`: If `true`, uses `IdentityHashMap` for reference equality instead of object equality. Defaults to `false`.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
IndexedHashSet() Constructs a new `IndexedHashSet`.
IndexedHashSet(boolean nullValuesAllowed) Constructs a new `IndexedHashSet` with the specified option.
IndexedHashSet(boolean nullValuesAllowed, boolean referenceEquality) Constructs a new `IndexedHashSet` with the specified options.
IndexedHashSet(java.util.Collection<? extends E> c) Constructs a new `IndexedHashSet` containing the elements of the specified collection.
IndexedHashSet(java.util.Collection<? extends E> c, boolean nullValuesAllowed) Constructs a new `IndexedHashSet` containing the elements of the specified collection, with the specified option.
IndexedHashSet(java.util.Collection<? extends E> c, boolean nullValuesAllowed, boolean referenceEquality) Constructs a new `IndexedHashSet` containing the elements of the specified collection, with the specified options.

Method Summary

Modifier and Type	Method and Description
boolean	add(E o)
void	add(int index, E o)
boolean	addAll(java.util.Collection<? extends E> c)
boolean	addAll(int index, java.util.Collection<? extends E> c)
void	clear()
boolean	contains(java.lang.Object o)
boolean	containsAll(java.util.Collection<?> c)
boolean	equals(java.lang.Object o)
E	first() Returns the first element in the set, or null if the set is empty
E	get(int index)
int	indexOf(java.lang.Object o)
boolean	isEmpty()
boolean	isNullValuesAllowed() Returns whether null values are allowed in the set
boolean	isReferenceEquality() Returns whether reference equality is being used instead of object equality
java.util.Iterator<E>	iterator()
E	last() Returns the last element in the set, or null if the set is empty
int	lastIndexOf(java.lang.Object o)
java.util.ListIterator<E>	listIterator()
java.util.ListIterator<E>	listIterator(int index)
void	readExternal(java.io.ObjectInput s)
E	remove(int index)
boolean	remove(java.lang.Object o)
boolean	removeAll(java.util.Collection<?> c)
boolean	retainAll(java.util.Collection<?> c)
E	set(int index, E o)
void	setNullValuesAllowed(boolean b) Sets whether null values are allowed in the set.
void	setReferenceEquality(boolean b) Sets whether to use reference equality instead of object equality
int	size()
java.util.Spliterator<E>	spliterator()
java.util.List<E>	subList(int fromIndex, int toIndex) This implementation throws an UnsupportedOperationException because it is not possible to efficiently implement a modifiable subList view for an IndexedHashSet.
IndexedHashSet<E>	testIntegrity() Performs integrity checks on the internal data structures for testing purposes
java.lang.Object[]	toArray()
<T> T[]	toArray(T[] a)
java.util.List<E>	toList() Returns an unmodifiable view of the list backing this set
void	truncateToSize(int toSize) Truncates the set to the specified size, removing elements from the end if necessary
void	writeExternal(java.io.ObjectOutput s)

Methods inherited from class java.lang.Object

getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.util.Set

hashCode

Methods inherited from interface java.util.List

hashCode, replaceAll, sort

Methods inherited from interface java.util.Collection

parallelStream, removeIf, stream

Methods inherited from interface java.lang.Iterable

forEach

Constructor Detail

IndexedHashSet

public IndexedHashSet()

Constructs a new `IndexedHashSet`. Null values are allowed in the set. Object equality is used.

IndexedHashSet

public IndexedHashSet(boolean nullValuesAllowed)

Constructs a new `IndexedHashSet` with the specified option. Object equality is used.

Parameters:

nullValuesAllowed - Whether null values are allowed in the set.

IndexedHashSet

public IndexedHashSet(boolean nullValuesAllowed,
                      boolean referenceEquality)

Constructs a new `IndexedHashSet` with the specified options.

Parameters:

nullValuesAllowed - Whether null values are allowed in the set.

referenceEquality - Whether to use reference equality instead of object equality.

IndexedHashSet

public IndexedHashSet(java.util.Collection<? extends E> c)

Constructs a new `IndexedHashSet` containing the elements of the specified collection. Null values are allowed in the set. Object equality is used.

Parameters:

c - The collection whose elements are to be placed into this set.

IndexedHashSet

public IndexedHashSet(java.util.Collection<? extends E> c,
                      boolean nullValuesAllowed)

Constructs a new `IndexedHashSet` containing the elements of the specified collection, with the specified option. Object equality is used.

Parameters:

c - The collection whose elements are to be placed into this set.

nullValuesAllowed - Whether null values are allowed in the set.

IndexedHashSet

public IndexedHashSet(java.util.Collection<? extends E> c,
                      boolean nullValuesAllowed,
                      boolean referenceEquality)

Constructs a new `IndexedHashSet` containing the elements of the specified collection, with the specified options.

Parameters:

c - The collection whose elements are to be placed into this set.

nullValuesAllowed - Whether null values are allowed in the set.

referenceEquality - Whether to use reference equality instead of object equality.

Method Detail

spliterator

public java.util.Spliterator<E> spliterator()

Specified by:

spliterator in interface java.lang.Iterable<E>

Specified by:

spliterator in interface java.util.Collection<E>

Specified by:

spliterator in interface java.util.List<E>

Specified by:

spliterator in interface java.util.Set<E>

setNullValuesAllowed

public void setNullValuesAllowed(boolean b)

Sets whether null values are allowed in the set.

Parameters:

b - `true` if null values are allowed, `false` otherwise.

Throws:

java.lang.IllegalStateException - If setting `nullValuesAllowed` to `false` while the set contains null elements.

isNullValuesAllowed

public boolean isNullValuesAllowed()

Returns whether null values are allowed in the set

Returns:

true if null values are allowed, false otherwise

setReferenceEquality

public void setReferenceEquality(boolean b)

Sets whether to use reference equality instead of object equality

Parameters:

b - true to use reference equality, false to use object equality

isReferenceEquality

public boolean isReferenceEquality()

Returns whether reference equality is being used instead of object equality

Returns:

true if reference equality is being used, false if object equality is being used

add

public boolean add(E o)

Specified by:

add in interface java.util.Collection<E>

Specified by:

add in interface java.util.List<E>

Specified by:

add in interface java.util.Set<E>

addAll

public boolean addAll(java.util.Collection<? extends E> c)

Specified by:

addAll in interface java.util.Collection<E>

Specified by:

addAll in interface java.util.List<E>

Specified by:

addAll in interface java.util.Set<E>

clear

public void clear()

Specified by:

clear in interface java.util.Collection<E>

Specified by:

clear in interface java.util.List<E>

Specified by:

clear in interface java.util.Set<E>

truncateToSize

public void truncateToSize(int toSize)

Truncates the set to the specified size, removing elements from the end if necessary

Parameters:

toSize - the new size of the set

contains

public boolean contains(java.lang.Object o)

Specified by:

contains in interface java.util.Collection<E>

Specified by:

contains in interface java.util.List<E>

Specified by:

contains in interface java.util.Set<E>

containsAll

public boolean containsAll(java.util.Collection<?> c)

Specified by:

containsAll in interface java.util.Collection<E>

Specified by:

containsAll in interface java.util.List<E>

Specified by:

containsAll in interface java.util.Set<E>

equals

public boolean equals(java.lang.Object o)

Specified by:

equals in interface java.util.Collection<E>

Specified by:

equals in interface java.util.List<E>

Specified by:

equals in interface java.util.Set<E>

Overrides:

equals in class java.lang.Object

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface java.util.Collection<E>

Specified by:

isEmpty in interface java.util.List<E>

Specified by:

isEmpty in interface java.util.Set<E>

iterator

public java.util.Iterator<E> iterator()

Specified by:

iterator in interface java.lang.Iterable<E>

Specified by:

iterator in interface java.util.Collection<E>

Specified by:

iterator in interface java.util.List<E>

Specified by:

iterator in interface java.util.Set<E>

remove

public boolean remove(java.lang.Object o)

Specified by:

remove in interface java.util.Collection<E>

Specified by:

remove in interface java.util.List<E>

Specified by:

remove in interface java.util.Set<E>

removeAll

public boolean removeAll(java.util.Collection<?> c)

Specified by:

removeAll in interface java.util.Collection<E>

Specified by:

removeAll in interface java.util.List<E>

Specified by:

removeAll in interface java.util.Set<E>

retainAll

public boolean retainAll(java.util.Collection<?> c)

Specified by:

retainAll in interface java.util.Collection<E>

Specified by:

retainAll in interface java.util.List<E>

Specified by:

retainAll in interface java.util.Set<E>

size

public int size()

Specified by:

size in interface java.util.Collection<E>

Specified by:

size in interface java.util.List<E>

Specified by:

size in interface java.util.Set<E>

toArray

public java.lang.Object[] toArray()

Specified by:

toArray in interface java.util.Collection<E>

Specified by:

toArray in interface java.util.List<E>

Specified by:

toArray in interface java.util.Set<E>

toArray

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

Specified by:

toArray in interface java.util.Collection<E>

Specified by:

toArray in interface java.util.List<E>

Specified by:

toArray in interface java.util.Set<E>

toList

public java.util.List<E> toList()

Returns an unmodifiable view of the list backing this set

Returns:

an unmodifiable view of the list backing this set

add

public void add(int index,
                E o)

Specified by:

add in interface java.util.List<E>

addAll

public boolean addAll(int index,
                      java.util.Collection<? extends E> c)

Specified by:

addAll in interface java.util.List<E>

first

public E first()

Returns the first element in the set, or null if the set is empty

Returns:

the first element in the set, or null if the set is empty

last

public E last()

Returns the last element in the set, or null if the set is empty

Returns:

the last element in the set, or null if the set is empty

get

public E get(int index)

Specified by:

get in interface java.util.List<E>

indexOf

public int indexOf(java.lang.Object o)

Specified by:

indexOf in interface java.util.List<E>

lastIndexOf

public int lastIndexOf(java.lang.Object o)

Specified by:

lastIndexOf in interface java.util.List<E>

listIterator

public java.util.ListIterator<E> listIterator()

Specified by:

listIterator in interface java.util.List<E>

listIterator

public java.util.ListIterator<E> listIterator(int index)

Specified by:

listIterator in interface java.util.List<E>

remove

public E remove(int index)

Specified by:

remove in interface java.util.List<E>

set

public E set(int index,
             E o)

Specified by:

set in interface java.util.List<E>

subList

public java.util.List<E> subList(int fromIndex,
                                 int toIndex)

This implementation throws an UnsupportedOperationException because it is not possible to efficiently implement a modifiable subList view for an IndexedHashSet. Allowing modifications to the subList would require building a special list implementation that understands it is backed by an IndexedHashSet, which would add significant complexity.

Specified by:

subList in interface java.util.List<E>

Throws:

java.lang.UnsupportedOperationException - always

testIntegrity

public IndexedHashSet<E> testIntegrity()

Performs integrity checks on the internal data structures for testing purposes

Returns:

this IndexedHashSet instance

Throws:

java.lang.IllegalStateException - if any integrity checks fail

writeExternal

public void writeExternal(java.io.ObjectOutput s)
                   throws java.io.IOException

Specified by:

writeExternal in interface java.io.Externalizable

Throws:

java.io.IOException

readExternal

public void readExternal(java.io.ObjectInput s)
                  throws java.io.IOException,
                         java.lang.ClassNotFoundException

Specified by:

readExternal in interface java.io.Externalizable

Throws:

java.io.IOException

java.lang.ClassNotFoundException