1 files changed, 129 insertions, 0 deletions
diff --git a/src/org/unitConverter/math/ZeroIsNullMap.java b/src/org/unitConverter/math/ZeroIsNullMap.java
new file mode 100644
index 0000000..10e4d52
--- /dev/null
+++ b/src/org/unitConverter/math/ZeroIsNullMap.java
@@ -0,0 +1,129 @@
+/**
+ * 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