From 72eed55d9f834de8302564fbe6dfa3d1d446afb4 Mon Sep 17 00:00:00 2001 From: Adrien Hopkins Date: Sat, 7 Aug 2021 15:25:54 -0500 Subject: Renamed sevenUnits.math to sevenUnits.utils --- .../utils/ConditionalExistenceCollections.java | 468 +++++++++++++++++++++ 1 file changed, 468 insertions(+) create mode 100644 src/main/java/sevenUnits/utils/ConditionalExistenceCollections.java (limited to 'src/main/java/sevenUnits/utils/ConditionalExistenceCollections.java') diff --git a/src/main/java/sevenUnits/utils/ConditionalExistenceCollections.java b/src/main/java/sevenUnits/utils/ConditionalExistenceCollections.java new file mode 100644 index 0000000..2adb579 --- /dev/null +++ b/src/main/java/sevenUnits/utils/ConditionalExistenceCollections.java @@ -0,0 +1,468 @@ +/** + * Copyright (C) 2019 Adrien Hopkins + * + * This program is free software: you can redistribute it and/or modify + * it under the terms of the GNU Affero General Public License as published by + * the Free Software Foundation, either version 3 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU Affero General Public License for more details. + * + * You should have received a copy of the GNU Affero General Public License + * along with this program. If not, see . + */ +package sevenUnits.utils; + +import java.util.AbstractCollection; +import java.util.AbstractMap; +import java.util.AbstractSet; +import java.util.Collection; +import java.util.Iterator; +import java.util.Map; +import java.util.Map.Entry; +import java.util.NoSuchElementException; +import java.util.Set; +import java.util.function.Predicate; + +/** + * Elements in these wrapper collections only exist if they pass a condition. + *

+ * All of the collections in this class are "views" of the provided collections. + * They are mutable if the provided collections are mutable, they allow null if + * the provided collections allow null, they will reflect changes in the + * provided collection, etc. + *

+ * The modification operations will always run the corresponding operations, + * even if the conditional existence collection doesn't change. For example, if + * you have a set that ignores even numbers, add(2) will still add a 2 to the + * backing set (but the conditional existence set will say it doesn't exist). + *

+ * The returned collections do not pass the hashCode and equals + * operations through to the backing collections, but rely on {@code Object}'s + * {@code equals} and {@code hashCode} methods. This is necessary to preserve + * the contracts of these operations in the case that the backing collections + * are sets or lists. + *

+ * Other than that, the only difference between the provided collections and + * the returned collections are that elements don't exist if they don't pass the + * provided condition. + * + * + * @author Adrien Hopkins + * @since 2019-10-17 + */ +// TODO add conditional existence Lists and Sorted/Navigable Sets/Maps +public final class ConditionalExistenceCollections { + /** + * Elements in this collection only exist if they meet a condition. + * + * @author Adrien Hopkins + * @since 2019-10-17 + * @param type of element in collection + */ + static final class ConditionalExistenceCollection + extends AbstractCollection { + final Collection collection; + final Predicate existenceCondition; + + /** + * Creates the {@code ConditionalExistenceCollection}. + * + * @param collection + * @param existenceCondition + * @since 2019-10-17 + */ + private ConditionalExistenceCollection(final Collection collection, + final Predicate existenceCondition) { + this.collection = collection; + this.existenceCondition = existenceCondition; + } + + @Override + public boolean add(final E e) { + return this.collection.add(e) && this.existenceCondition.test(e); + } + + @Override + public void clear() { + this.collection.clear(); + } + + @Override + public boolean contains(final Object o) { + if (!this.collection.contains(o)) + return false; + + // this collection can only contain instances of E + // since the object is in the collection, we know that it must be an + // instance of E + // therefore this cast will always work + @SuppressWarnings("unchecked") + final E e = (E) o; + + return this.existenceCondition.test(e); + } + + @Override + public Iterator iterator() { + return conditionalExistenceIterator(this.collection.iterator(), + this.existenceCondition); + } + + @Override + public boolean remove(final Object o) { + // remove() must be first in the && statement, otherwise it may not + // execute + final boolean containedObject = this.contains(o); + return this.collection.remove(o) && containedObject; + } + + @Override + public int size() { + return (int) this.collection.stream().filter(this.existenceCondition) + .count(); + } + + @Override + public Object[] toArray() { + // ensure the toArray operation is supported + this.collection.toArray(); + + // if it works, do it for real + return super.toArray(); + } + + @Override + public T[] toArray(T[] a) { + // ensure the toArray operation is supported + this.collection.toArray(); + + // if it works, do it for real + return super.toArray(a); + } + } + + /** + * Elements in this wrapper iterator only exist if they pass a condition. + * + * @author Adrien Hopkins + * @since 2019-10-17 + * @param type of elements in iterator + */ + static final class ConditionalExistenceIterator implements Iterator { + final Iterator iterator; + final Predicate existenceCondition; + E nextElement; + boolean hasNext; + + /** + * Creates the {@code ConditionalExistenceIterator}. + * + * @param iterator + * @param condition + * @since 2019-10-17 + */ + private ConditionalExistenceIterator(final Iterator iterator, + final Predicate condition) { + this.iterator = iterator; + this.existenceCondition = condition; + this.getAndSetNextElement(); + } + + /** + * Gets the next element, and sets nextElement and hasNext accordingly. + * + * @since 2019-10-17 + */ + private void getAndSetNextElement() { + do { + if (!this.iterator.hasNext()) { + this.nextElement = null; + this.hasNext = false; + return; + } + this.nextElement = this.iterator.next(); + } while (!this.existenceCondition.test(this.nextElement)); + this.hasNext = true; + } + + @Override + public boolean hasNext() { + return this.hasNext; + } + + @Override + public E next() { + if (this.hasNext()) { + final E next = this.nextElement; + this.getAndSetNextElement(); + return next; + } else + throw new NoSuchElementException(); + } + + @Override + public void remove() { + this.iterator.remove(); + } + } + + /** + * Mappings in this map only exist if the entry passes some condition. + * + * @author Adrien Hopkins + * @since 2019-10-17 + * @param key type + * @param value type + */ + static final class ConditionalExistenceMap extends AbstractMap { + Map map; + Predicate> entryExistenceCondition; + + /** + * Creates the {@code ConditionalExistenceMap}. + * + * @param map + * @param entryExistenceCondition + * @since 2019-10-17 + */ + private ConditionalExistenceMap(final Map map, + final Predicate> entryExistenceCondition) { + this.map = map; + this.entryExistenceCondition = entryExistenceCondition; + } + + @Override + public boolean containsKey(final Object key) { + if (!this.map.containsKey(key)) + return false; + + // only instances of K have mappings in the backing map + // since we know that key is a valid key, it must be an instance of K + @SuppressWarnings("unchecked") + final K keyAsK = (K) key; + + // get and test entry + final V value = this.map.get(key); + final Entry entry = new SimpleEntry<>(keyAsK, value); + return this.entryExistenceCondition.test(entry); + } + + @Override + public Set> entrySet() { + return conditionalExistenceSet(this.map.entrySet(), + this.entryExistenceCondition); + } + + @Override + public V get(final Object key) { + return this.containsKey(key) ? this.map.get(key) : null; + } + + private final Entry getEntry(K key) { + return new Entry<>() { + @Override + public K getKey() { + return key; + } + + @Override + public V getValue() { + return ConditionalExistenceMap.this.map.get(key); + } + + @Override + public V setValue(V value) { + return ConditionalExistenceMap.this.map.put(key, value); + } + }; + } + + @Override + public Set keySet() { + return conditionalExistenceSet(super.keySet(), + k -> this.entryExistenceCondition.test(this.getEntry(k))); + } + + @Override + public V put(final K key, final V value) { + final V oldValue = this.map.put(key, value); + + // get and test entry + final Entry entry = new SimpleEntry<>(key, oldValue); + return this.entryExistenceCondition.test(entry) ? oldValue : null; + } + + @Override + public V remove(final Object key) { + final V oldValue = this.map.remove(key); + return this.containsKey(key) ? oldValue : null; + } + + @Override + public Collection values() { + // maybe change this to use ConditionalExistenceCollection + return super.values(); + } + } + + /** + * Elements in this set only exist if a certain condition is true. + * + * @author Adrien Hopkins + * @since 2019-10-17 + * @param type of element in set + */ + static final class ConditionalExistenceSet extends AbstractSet { + private final Set set; + private final Predicate existenceCondition; + + /** + * Creates the {@code ConditionalNonexistenceSet}. + * + * @param set set to use + * @param existenceCondition condition where element exists + * @since 2019-10-17 + */ + private ConditionalExistenceSet(final Set set, + final Predicate existenceCondition) { + this.set = set; + this.existenceCondition = existenceCondition; + } + + /** + * {@inheritDoc} + *

+ * Note that this method returns {@code false} if {@code e} does not pass + * the existence condition. + */ + @Override + public boolean add(final E e) { + return this.set.add(e) && this.existenceCondition.test(e); + } + + @Override + public void clear() { + this.set.clear(); + } + + @Override + public boolean contains(final Object o) { + if (!this.set.contains(o)) + return false; + + // this set can only contain instances of E + // since the object is in the set, we know that it must be an instance + // of E + // therefore this cast will always work + @SuppressWarnings("unchecked") + final E e = (E) o; + + return this.existenceCondition.test(e); + } + + @Override + public Iterator iterator() { + return conditionalExistenceIterator(this.set.iterator(), + this.existenceCondition); + } + + @Override + public boolean remove(final Object o) { + // remove() must be first in the && statement, otherwise it may not + // execute + final boolean containedObject = this.contains(o); + return this.set.remove(o) && containedObject; + } + + @Override + public int size() { + return (int) this.set.stream().filter(this.existenceCondition).count(); + } + + @Override + public Object[] toArray() { + // ensure the toArray operation is supported + this.set.toArray(); + + // if it works, do it for real + return super.toArray(); + } + + @Override + public T[] toArray(T[] a) { + // ensure the toArray operation is supported + this.set.toArray(); + + // if it works, do it for real + return super.toArray(a); + } + } + + /** + * Elements in the returned wrapper collection are ignored if they don't pass + * a condition. + * + * @param type of elements in collection + * @param collection collection to wrap + * @param existenceCondition elements only exist if this returns true + * @return wrapper collection + * @since 2019-10-17 + */ + public static final Collection conditionalExistenceCollection( + final Collection collection, + final Predicate existenceCondition) { + return new ConditionalExistenceCollection<>(collection, + existenceCondition); + } + + /** + * Elements in the returned wrapper iterator are ignored if they don't pass a + * condition. + * + * @param type of elements in iterator + * @param iterator iterator to wrap + * @param existenceCondition elements only exist if this returns true + * @return wrapper iterator + * @since 2019-10-17 + */ + public static final Iterator conditionalExistenceIterator( + final Iterator iterator, final Predicate existenceCondition) { + return new ConditionalExistenceIterator<>(iterator, existenceCondition); + } + + /** + * Mappings in the returned wrapper map are ignored if the corresponding + * entry doesn't pass a condition + * + * @param type of key in map + * @param type of value in map + * @param map map to wrap + * @param entryExistenceCondition mappings only exist if this returns true + * @return wrapper map + * @since 2019-10-17 + */ + public static final Map conditionalExistenceMap( + final Map map, + final Predicate> entryExistenceCondition) { + return new ConditionalExistenceMap<>(map, entryExistenceCondition); + } + + /** + * Elements in the returned wrapper set are ignored if they don't pass a + * condition. + * + * @param type of elements in set + * @param set set to wrap + * @param existenceCondition elements only exist if this returns true + * @return wrapper set + * @since 2019-10-17 + */ + public static final Set conditionalExistenceSet(final Set set, + final Predicate existenceCondition) { + return new ConditionalExistenceSet<>(set, existenceCondition); + } +} -- cgit v1.2.3