io.permazen.util.AbstractNavigableSet Maven / Gradle / Ivy
/*
* Copyright (C) 2015 Archie L. Cobbs. All rights reserved.
*/
package io.permazen.util;
import com.google.common.base.Preconditions;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NavigableSet;
import java.util.NoSuchElementException;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;
/**
* Support superclass for {@link NavigableSet} implementations for which calculating {@link #size size()} requires
* an iteration through all of the set's elements to count them.
*
*
* For a read-only implementation, subclasses should implement {@link #comparator comparator()}, {@link #contains contains()},
* {@link #iterator iterator()}, and {@link #createSubSet createSubSet()} to handle reversed and restricted range sub-sets.
*
*
* For a mutable implementation, subclasses should also implement {@link #add add()}, {@link #remove remove()},
* {@link #clear clear()}, and make the {@link #iterator iterator()} mutable.
*
*
* All overridden methods must be aware of the {@linkplain #bounds range restriction bounds}, if any.
*
* @param element type
*/
public abstract class AbstractNavigableSet extends AbstractIterationSet implements NavigableSet {
/**
* Element range bounds associated with this instance.
*/
protected final Bounds bounds;
/**
* Convenience constructor for the case where there are no lower or upper bounds.
*/
protected AbstractNavigableSet() {
this(new Bounds<>());
}
/**
* Primary constructor.
*
* @param bounds range restriction
* @throws IllegalArgumentException if {@code bounds} is null
*/
protected AbstractNavigableSet(Bounds bounds) {
Preconditions.checkArgument(bounds != null, "null bounds");
this.bounds = bounds;
}
/**
* Removes the given element from this set if it is present.
*
*
* The implementation in {@link AbstractNavigableSet} always throws {@link UnsupportedOperationException}.
*/
@Override
public boolean remove(Object elem) {
throw new UnsupportedOperationException("read-only set");
}
@Override
public E first() {
return this.iterator().next();
}
@Override
public E last() {
return this.descendingIterator().next();
}
@Override
public E pollFirst() {
final Iterator i = this.iterator();
if (!i.hasNext())
return null;
final E value = i.next();
i.remove();
return value;
}
@Override
public E pollLast() {
return this.descendingSet().pollFirst();
}
@Override
public Iterator descendingIterator() {
return this.descendingSet().iterator();
}
@Override
public E lower(E elem) {
return this.searchBelow(elem, false);
}
@Override
public E floor(E elem) {
return this.searchBelow(elem, true);
}
@Override
public E ceiling(E elem) {
return this.searchAbove(elem, true);
}
@Override
public E higher(E elem) {
return this.searchAbove(elem, false);
}
@Override
public NavigableSet headSet(E newMaxElement) {
return this.headSet(newMaxElement, false);
}
@Override
public NavigableSet tailSet(E newMinElement) {
return this.tailSet(newMinElement, true);
}
@Override
public NavigableSet subSet(E newMinElement, E newMaxElement) {
return this.subSet(newMinElement, true, newMaxElement, false);
}
@Override
public NavigableSet descendingSet() {
return this.createSubSet(true, this.bounds.reverse());
}
@Override
public NavigableSet headSet(E newMaxElement, boolean inclusive) {
final Bounds newBounds = this.bounds.withUpperBound(newMaxElement, BoundType.of(inclusive));
if (!this.bounds.isWithinBounds(this.comparator(), newBounds))
throw new IllegalArgumentException("upper bound " + newMaxElement + " is out of bounds: " + this.bounds);
return this.createSubSet(false, newBounds);
}
@Override
public NavigableSet tailSet(E newMinElement, boolean inclusive) {
final Bounds newBounds = this.bounds.withLowerBound(newMinElement, BoundType.of(inclusive));
if (!this.bounds.isWithinBounds(this.comparator(), newBounds))
throw new IllegalArgumentException("lower bound " + newMinElement + " is out of bounds: " + this.bounds);
return this.createSubSet(false, newBounds);
}
@Override
public NavigableSet subSet(E newMinElement, boolean minInclusive, E newMaxElement, boolean maxInclusive) {
final Bounds newBounds = new Bounds<>(newMinElement,
BoundType.of(minInclusive), newMaxElement, BoundType.of(maxInclusive));
if (!this.bounds.isWithinBounds(this.comparator(), newBounds))
throw new IllegalArgumentException("new bound(s) " + newBounds + " are out of bounds: " + this.bounds);
return this.createSubSet(false, newBounds);
}
@Override
public Spliterator spliterator() {
return new Spliterators.AbstractSpliterator(Long.MAX_VALUE,
Spliterator.ORDERED | Spliterator.SORTED | Spliterator.DISTINCT) {
private final Iterator iterator = AbstractNavigableSet.this.iterator();
@Override
public boolean tryAdvance(Consumer action) {
if (!this.iterator.hasNext())
return false;
action.accept(iterator.next());
return true;
}
@Override
public Comparator getComparator() {
return AbstractNavigableSet.this.comparator();
}
};
}
/**
* Search for a lower element. Used to implement {@link #floor floor()} and {@link #lower lower()}.
*
*
* The implementation in {@link AbstractNavigableSet} checks the bounds then returns the first element from a head set.
*
* @param elem upper limit for search
* @param inclusive true if {@code elem} itself is a candidate
* @return highest element below {@code elem}, or null if not found
*/
protected E searchBelow(E elem, boolean inclusive) {
if (!this.isWithinLowerBound(elem))
return null;
final NavigableSet subSet = this.isWithinUpperBound(elem) ? this.headSet(elem, inclusive) : this;
try {
return subSet.last();
} catch (NoSuchElementException e) {
return null;
}
}
/**
* Search for a higher element. Used to implement {@link #ceiling ceiling()} and {@link #higher higher()}.
*
*
* The implementation in {@link AbstractNavigableSet} checks the bounds then returns the first element from a tail set.
*
* @param elem lower limit for search
* @param inclusive true if {@code elem} itself is a candidate
* @return lowest element above {@code elem}, or null if not found
*/
protected E searchAbove(E elem, boolean inclusive) {
if (!this.isWithinUpperBound(elem))
return null;
final NavigableSet subSet = this.isWithinLowerBound(elem) ? this.tailSet(elem, inclusive) : this;
try {
return subSet.first();
} catch (NoSuchElementException e) {
return null;
}
}
/**
* Get a non-null {@link Comparator} that sorts consistently with, and optionally reversed from, this instance.
*
* @param reversed whether to return a reversed {@link Comparator}
* @return a non-null {@link Comparator}
*/
protected Comparator getComparator(boolean reversed) {
return NavigableSets.getComparator(this.comparator(), reversed);
}
/**
* Create a (possibly reversed) view of this instance with (possibly) tighter lower and/or upper bounds.
* The {@code newBounds} are consistent with the new ordering (i.e., reversed relative to this instance's ordering if
* {@code reverse} is true) and have already been range-checked against {@linkplain #bounds this instance's current bounds}.
*
* @param reverse whether the new set's ordering should be reversed relative to this instance's ordering
* @param newBounds new bounds
* @return restricted and/or reversed view of this instance
* @throws IllegalArgumentException if {@code newBounds} is null
* @throws IllegalArgumentException if a bound in {@code newBounds} is null and this set does not permit null elements
*/
protected abstract NavigableSet createSubSet(boolean reverse, Bounds newBounds);
/**
* Determine if the given element is within this instance's lower bound (if any).
*
*
* The implementation in {@link AbstractNavigableSet} returns {@code this.bounds.isWithinLowerBound(this.comparator(), elem)}.
*
* @param elem set element
* @return true if {@code elem} is within this instance's lower bound, or this instance has no lower bound
*/
protected boolean isWithinLowerBound(E elem) {
return this.bounds.isWithinLowerBound(this.comparator(), elem);
}
/**
* Determine if the given element is within this instance's upper bound (if any).
*
*
* The implementation in {@link AbstractNavigableSet} returns {@code this.bounds.isWithinUpperBound(this.comparator(), elem)}.
*
* @param elem set element
* @return true if {@code elem} is within this instance's upper bound, or this instance has no upper bound
*/
protected boolean isWithinUpperBound(E elem) {
return this.bounds.isWithinUpperBound(this.comparator(), elem);
}
}