Package io.permazen.util

Class AbstractIterationSet<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractSet<E>

io.permazen.util.AbstractIterationSet<E>

All Implemented Interfaces:

Iterable<E>, Collection<E>, Set<E>

Direct Known Subclasses:

AbstractNavigableSet, ConvertedSet

public abstract class AbstractIterationSet<E>
extends AbstractSet<E>

Support superclass for Set implementations based on database entries.

This class assumes the following:

• The size of the set is not cached, i.e., it requires an actual enumeration of all of the set's elements; and
• Iteration may utilize a resource that needs to be closed

As a result:

• AbstractSet methods that rely on size() are overridden with implementations that avoid the use of size() where possible; and
• iterator() returns a CloseableIterator
• stream(), which is based on iterator(), arranges (via Stream.onClose()) for the iterator to be closed on Stream.close().

To be safe, try-with-resources should be used with iterator() and stream().

For a read-only implementation, subclasses should implement contains() and iterator().

For a mutable implementation, subclasses should also implement add(), remove(), and clear(), and make the iterator() mutable.

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	AbstractIterationSet()

Method Summary

Modifier and Type	Method	Description
protected Spliterator<E>	buildSpliterator(Iterator<E> iterator)	Build a Spliterator appropriate for this set from the given instance iterator.
boolean	equals(Object obj)	Overridden in AbstractIterationSet to minimize the use of size().
int	hashCode()
boolean	isEmpty()	Overridden in AbstractIterationSet to minimize the use of size().
abstract CloseableIterator<E>	iterator()
int	size()	Calculate size.
Spliterator<E>	spliterator()	Overridden in AbstractIterationSet to avoid the use of size().
Stream<E>	stream()
Object[]	toArray()	Overridden in AbstractIterationSet to minimize the use of size().
<T> T[]	toArray(T[] array)	Overridden in AbstractIterationSet to minimize the use of size().

Methods inherited from class java.util.AbstractSet

removeAll

Methods inherited from class java.util.AbstractCollection

add, addAll, clear, contains, containsAll, remove, retainAll, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection

parallelStream, removeIf, toArray

Methods inherited from interface java.lang.Iterable

forEach

Methods inherited from interface java.util.Set

add, addAll, clear, contains, containsAll, remove, retainAll

Constructor Details

AbstractIterationSet

protected AbstractIterationSet()

Method Details

iterator

public abstract CloseableIterator<E> iterator()

Specified by:

iterator in interface Collection<E>

Specified by:

iterator in interface Iterable<E>

Specified by:

iterator in interface Set<E>

Specified by:

iterator in class AbstractCollection<E>

size

public int size()

Calculate size.

The implementation in AbstractIterationSet iterates through all of the elements.

Specified by:

size in interface Collection<E>

Specified by:

size in interface Set<E>

Specified by:

size in class AbstractCollection<E>

equals

public boolean equals(Object obj)

Overridden in AbstractIterationSet to minimize the use of size().

Specified by:

equals in interface Collection<E>

Specified by:

equals in interface Set<E>

Overrides:

equals in class AbstractSet<E>

hashCode

public int hashCode()

Specified by:

hashCode in interface Collection<E>

Specified by:

hashCode in interface Set<E>

Overrides:

hashCode in class AbstractSet<E>

isEmpty

public boolean isEmpty()

Overridden in AbstractIterationSet to minimize the use of size().

Specified by:

isEmpty in interface Collection<E>

Specified by:

isEmpty in interface Set<E>

Overrides:

isEmpty in class AbstractCollection<E>

toArray

public Object[] toArray()

Overridden in AbstractIterationSet to minimize the use of size().

Specified by:

toArray in interface Collection<E>

Specified by:

toArray in interface Set<E>

Overrides:

toArray in class AbstractCollection<E>

toArray

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

Overridden in AbstractIterationSet to minimize the use of size().

Specified by:

toArray in interface Collection<E>

Specified by:

toArray in interface Set<E>

Overrides:

toArray in class AbstractCollection<E>

spliterator

public Spliterator<E> spliterator()

Overridden in AbstractIterationSet to avoid the use of size().

Note: the underlying CloseableIterator is not closed when this method is used. Prefer using buildSpliterator(java.util.Iterator<E>) and arranging for the iterator to be closed separately.

buildSpliterator

protected Spliterator<E> buildSpliterator(Iterator<E> iterator)

Build a Spliterator appropriate for this set from the given instance iterator.

Implementations should probably use Spliterators.spliteratorUnknownSize() unless the size is known.

Parameters:

iterator - a new iterator returned from {#link #iterator}

stream

public Stream<E> stream()

The implementation in AbstractIterationSet build a stream from the results from iterator() and buildSpliterator(), and marks the iterator for close via Stream.onClose().