4 files changed, 372 insertions, 132 deletions

diff --git a/src/org/unitConverter/math/ConditionalExistenceCollections.java b/src/org/unitConverter/math/ConditionalExistenceCollections.java
new file mode 100644
index 0000000..c0a69f0
--- /dev/null
+++ b/src/org/unitConverter/math/ConditionalExistenceCollections.java
@@ -0,0 +1,322 @@
+/**
+ * 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 <https://www.gnu.org/licenses/>.
+ */
+package org.unitConverter.math;
+
+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.
+ * <p>
+ * 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.
+ * <p>
+ * 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).
+ * <p>
+ * The returned collections do <i>not</i> 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.
+ * <p>
+ * Other than that, <i>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</i>.
+ * 
+ * 
+ * @author Adrien Hopkins
+ * @since 2019-10-17
+ */
+// TODO add conditional existence Collections, Lists and Sorted/Navigable Sets/Maps
+public final class ConditionalExistenceCollections {
+	/**
+	 * Elements in this wrapper iterator only exist if they pass a condition.
+	 * 
+	 * @author Adrien Hopkins
+	 * @since 2019-10-17
+	 * @param <E>
+	 *            type of elements in iterator
+	 */
+	static final class ConditionalExistenceIterator<E> implements Iterator<E> {
+		final Iterator<E> iterator;
+		final Predicate<E> existenceCondition;
+		E nextElement;
+		boolean hasNext;
+
+		/**
+		 * Creates the {@code ConditionalExistenceIterator}.
+		 * 
+		 * @param iterator
+		 * @param condition
+		 * @since 2019-10-17
+		 */
+		private ConditionalExistenceIterator(final Iterator<E> iterator, final Predicate<E> 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 <K>
+	 *            key type
+	 * @param <V>
+	 *            value type
+	 */
+	static final class ConditionalExistenceMap<K, V> extends AbstractMap<K, V> {
+		Map<K, V> map;
+		Predicate<Entry<K, V>> entryExistenceCondition;
+
+		/**
+		 * Creates the {@code ConditionalExistenceMap}.
+		 * 
+		 * @param map
+		 * @param entryExistenceCondition
+		 * @since 2019-10-17
+		 */
+		private ConditionalExistenceMap(final Map<K, V> map, final Predicate<Entry<K, V>> 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<K, V> entry = new SimpleEntry<>(keyAsK, value);
+			return this.entryExistenceCondition.test(entry);
+		}
+
+		@Override
+		public Set<Entry<K, V>> entrySet() {
+			return conditionalExistenceSet(this.map.entrySet(), this.entryExistenceCondition);
+		}
+
+		@Override
+		public V get(final Object key) {
+			return this.containsKey(key) ? this.map.get(key) : null;
+		}
+
+		@Override
+		public Set<K> keySet() {
+			// maybe change this to use ConditionalExistenceSet
+			return super.keySet();
+		}
+
+		@Override
+		public V put(final K key, final V value) {
+			final V oldValue = this.map.put(key, value);
+
+			// get and test entry
+			final Entry<K, V> 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<V> 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 <E>
+	 *            type of element in set
+	 */
+	static final class ConditionalExistenceSet<E> extends AbstractSet<E> {
+		private final Set<E> set;
+		private final Predicate<E> existenceCondition;
+
+		/**
+		 * Creates the {@code ConditionalNonexistenceSet}.
+		 * 
+		 * @param set
+		 *            set to use
+		 * @param existenceCondition
+		 *            condition where element exists
+		 * @since 2019-10-17
+		 */
+		private ConditionalExistenceSet(final Set<E> set, final Predicate<E> existenceCondition) {
+			this.set = set;
+			this.existenceCondition = existenceCondition;
+		}
+
+		/**
+		 * {@inheritDoc}
+		 * <p>
+		 * 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<E> iterator() {
+			return conditionalExistenceIterator(this.set.iterator(), this.existenceCondition);
+		}
+
+		@Override
+		public boolean remove(final Object o) {
+			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();
+		}
+	}
+
+	/**
+	 * Elements in the returned wrapper iterator are ignored if they don't pass a condition.
+	 * 
+	 * @param <E>
+	 *            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 <E> Iterator<E> conditionalExistenceIterator(final Iterator<E> iterator,
+			final Predicate<E> existenceCondition) {
+		return new ConditionalExistenceIterator<>(iterator, existenceCondition);
+	}
+
+	/**
+	 * Mappings in the returned wrapper map are ignored if the corresponding entry doesn't pass a condition
+	 * 
+	 * @param <K>
+	 *            type of key in map
+	 * @param <V>
+	 *            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 <K, V> Map<K, V> conditionalExistenceMap(final Map<K, V> map,
+			final Predicate<Entry<K, V>> entryExistenceCondition) {
+		return new ConditionalExistenceMap<>(map, entryExistenceCondition);
+	}
+
+	/**
+	 * Elements in the returned wrapper set are ignored if they don't pass a condition.
+	 * 
+	 * @param <E>
+	 *            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 <E> Set<E> conditionalExistenceSet(final Set<E> set, final Predicate<E> existenceCondition) {
+		return new ConditionalExistenceSet<>(set, existenceCondition);
+	}
+}
diff --git a/src/org/unitConverter/math/ZeroIsNullMapTest.java b/src/org/unitConverter/math/ConditionalExistenceCollectionsTest.java
index c3db951..311ace5 100644
--- a/src/org/unitConverter/math/ZeroIsNullMapTest.java
+++ b/src/org/unitConverter/math/ConditionalExistenceCollectionsTest.java
@@ -18,21 +18,45 @@ package org.unitConverter.math;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import java.util.Arrays;
 import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.NoSuchElementException;
 
 import org.junit.jupiter.api.Test;
+import org.unitConverter.math.ConditionalExistenceCollections.ConditionalExistenceIterator;
 
 /**
+ * Tests the {@link #ConditionalExistenceCollections}.
+ * 
  * @author Adrien Hopkins
  * @since 2019-10-16
  */
-class ZeroIsNullMapTest {
+class ConditionalExistenceCollectionsTest {
 
 	/**
+	 * The returned iterator ignores elements that don't start with "a".
+	 * 
+	 * @return test iterator
+	 * @since 2019-10-17
+	 */
+	ConditionalExistenceIterator<String> getTestIterator() {
+		final List<String> items = Arrays.asList("aa", "ab", "ba");
+		final Iterator<String> it = items.iterator();
+		final ConditionalExistenceIterator<String> cit = (ConditionalExistenceIterator<String>) ConditionalExistenceCollections
+				.conditionalExistenceIterator(it, s -> s.startsWith("a"));
+		return cit;
+	}
+
+	/**
+	 * The returned map ignores mappings where the value is zero.
+	 * 
 	 * @return map to be used for test data
 	 * @since 2019-10-16
 	 */
@@ -42,7 +66,9 @@ class ZeroIsNullMapTest {
 		map.put("two", 2);
 		map.put("zero", 0);
 		map.put("ten", 10);
-		return ZeroIsNullMap.create(map);
+		final Map<String, Integer> conditionalMap = ConditionalExistenceCollections.conditionalExistenceMap(map,
+				e -> !Integer.valueOf(0).equals(e.getValue()));
+		return conditionalMap;
 	}
 
 	/**
@@ -92,6 +118,26 @@ class ZeroIsNullMapTest {
 		assertEquals(null, map.get("zero"));
 	}
 
+	@Test
+	void testIterator() {
+		final ConditionalExistenceIterator<String> testIterator = this.getTestIterator();
+
+		assertTrue(testIterator.hasNext);
+		assertTrue(testIterator.hasNext());
+		assertEquals("aa", testIterator.nextElement);
+		assertEquals("aa", testIterator.next());
+
+		assertTrue(testIterator.hasNext);
+		assertTrue(testIterator.hasNext());
+		assertEquals("ab", testIterator.nextElement);
+		assertEquals("ab", testIterator.next());
+
+		assertFalse(testIterator.hasNext);
+		assertFalse(testIterator.hasNext());
+		assertEquals(null, testIterator.nextElement);
+		assertThrows(NoSuchElementException.class, testIterator::next);
+	}
+
 	/**
 	 * Test method for {@link org.unitConverter.math.ZeroIsNullMap#keySet()}.
 	 */
diff --git a/src/org/unitConverter/math/ObjectProduct.java b/src/org/unitConverter/math/ObjectProduct.java
index 21ab207..0cf89ec 100644
--- a/src/org/unitConverter/math/ObjectProduct.java
+++ b/src/org/unitConverter/math/ObjectProduct.java
@@ -92,7 +92,8 @@ public final class ObjectProduct<T> {
 	 * @since 2019-10-16

 	 */

 	private ObjectProduct(final Map<T, Integer> exponents) {

-		this.exponents = Collections.unmodifiableMap(ZeroIsNullMap.create(new HashMap<>(exponents)));

+		this.exponents = Collections.unmodifiableMap(ConditionalExistenceCollections

+				.conditionalExistenceMap(new HashMap<>(exponents), e -> !Integer.valueOf(0).equals(e.getValue())));

 	}

 

 	/**

diff --git a/src/org/unitConverter/math/ZeroIsNullMap.java b/src/org/unitConverter/math/ZeroIsNullMap.java
deleted file mode 100644
index 10e4d52..0000000
--- a/src/org/unitConverter/math/ZeroIsNullMap.java
+++ /dev/null
@@ -1,129 +0,0 @@
-/**
- * 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 <https://www.gnu.org/licenses/>.
- */
-package org.unitConverter.math;
-
-import java.util.AbstractMap;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Map;
-import java.util.Objects;
-import java.util.Set;
-
-/**
- * A "wrapper" for an existing map that treats a zero value as equivalent to null.
- * 
- * @author Adrien Hopkins
- * @since 2019-10-16
- * @param <T>
- *            type of key
- */
-public final class ZeroIsNullMap<T> extends AbstractMap<T, Integer> {
-	/**
-	 * Create a ZeroIsNullMap. This method always creates a new map.
-	 * 
-	 * @param <T>
-	 *            type of key
-	 * @param map
-	 *            map to input
-	 * @return map that treats zero as null
-	 * @throws NullPointerException
-	 *             if map is null
-	 * @since 2019-10-16
-	 */
-	public static <T> Map<T, Integer> create(final Map<T, Integer> map) {
-		return new ZeroIsNullMap<>(Objects.requireNonNull(map, "map must not be null."));
-	}
-
-	private final Map<T, Integer> map;
-
-	/**
-	 * Creates the {@code ObjectProductMap}.
-	 * 
-	 * @param map
-	 * @since 2019-10-16
-	 */
-	private ZeroIsNullMap(final Map<T, Integer> map) {
-		this.map = map;
-	}
-
-	@Override
-	public void clear() {
-		this.map.clear();
-	}
-
-	@Override
-	public boolean containsKey(final Object key) {
-		return this.map.containsKey(key) && this.map.get(key) != 0;
-	}
-
-	@Override
-	public boolean containsValue(final Object value) {
-		return this.values().contains(value);
-	}
-
-	@Override
-	public Set<Entry<T, Integer>> entrySet() {
-		final Set<Entry<T, Integer>> entrySet = new HashSet<>(this.map.entrySet());
-		entrySet.removeIf(e -> e.getValue() == 0);
-		return entrySet;
-	}
-
-	@Override
-	public Integer get(final Object key) {
-		final Integer i = this.map.get(key);
-		if (Objects.equals(i, 0))
-			return null;
-		else
-			return i;
-	}
-
-	@Override
-	public Set<T> keySet() {
-		final Set<T> keySet = new HashSet<>(this.map.keySet());
-		keySet.removeIf(k -> this.map.get(k) == 0);
-		return keySet;
-	}
-
-	@Override
-	public Integer put(final T key, final Integer value) {
-		if (value != 0)
-			return this.map.put(key, value);
-		else
-			return null;
-	}
-
-	@Override
-	public void putAll(final Map<? extends T, ? extends Integer> m) {
-		for (final T key : m.keySet()) {
-			this.put(key, m.get(key));
-		}
-	}
-
-	@Override
-	public Integer remove(final Object key) {
-		return this.map.remove(key);
-	}
-
-	@Override
-	public Collection<Integer> values() {
-		final List<Integer> values = new ArrayList<>(this.map.values());
-		values.removeIf(i -> i == 0);
-		return values;
-	}
-}
\ No newline at end of file