Implemented a Map that can store multiple values per key.

src/zutil/struct/MultiMap.java

@@ -0,0 +1,189 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2020 Ziver Koc
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package zutil.struct;
+
+import java.lang.reflect.InvocationTargetException;
+import java.util.*;
+
+/**
+ * A Map wrapping object that allows supports for multiple values per key.
+ *
+ * @param <K> – the type of keys maintained by this map
+ * @param <V> – the type of mapped values
+ */
+public class MultiMap<K,V> implements Map<K,V> {
+
+    private Map<K, LinkedList<V>> internalMap;
+
+
+    /**
+     * Creates a MultiMap
+     */
+    public MultiMap() {
+         this.internalMap = new HashMap<>();
+    }
+
+    /**
+     * Creates a MultiMap
+     *
+     * @param internalMapClass   Provide the type of the internal map.
+     */
+    public MultiMap(Class<? extends Map> internalMapClass) throws IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException {
+        this.internalMap = internalMapClass.getDeclaredConstructor().newInstance();
+    }
+
+
+    /**
+     * @return the number of keys registered in the Map. Note that the number
+     *          of values contained might be more than the value returned here.
+     */
+    @Override
+    public int size() {
+        return internalMap.size();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return internalMap.isEmpty();
+    }
+
+    @Override
+    public boolean containsKey(Object key) {
+        return internalMap.containsKey(key);
+    }
+
+    @Override
+    public boolean containsValue(Object value) {
+        for (K key : internalMap.keySet()) {
+            for (V keyValue : internalMap.get(key)){
+                if (Objects.equals(value, keyValue))
+                    return true;
+            }
+        }
+
+        return false;
+    }
+
+
+    @Override
+    public V put(K key, V value) {
+        if (value == null) {
+            remove(key);
+            return null;
+        }
+
+        LinkedList<V> valueList = internalMap.get(key);
+
+        if (valueList == null) {
+            valueList = new LinkedList<V>();
+            internalMap.put(key, valueList);
+        }
+
+        V prevValue = (valueList.isEmpty() ? null : valueList.getLast());
+        valueList.add(value);
+
+        return prevValue;
+    }
+
+    @Override
+    public void putAll(Map<? extends K, ? extends V> m) {
+        if (m instanceof MultiMap) {
+            for (K key : m.keySet()) {
+                for (V value : ((MultiMap<? extends K, ? extends V>) m).getAll(key)){
+                    put(key, value);
+                }
+            }
+        } else {
+            for (Entry<? extends K, ? extends V> e : m.entrySet()) {
+                put(e.getKey(), e.getValue());
+            }
+        }
+    }
+
+    @Override
+    public V remove(Object key) {
+        if (key == null) {
+            return null;
+        }
+
+        LinkedList<V> valueList = internalMap.remove(key);
+
+        if (valueList != null)
+            return valueList.getFirst();
+        else
+            return null;
+    }
+
+    @Override
+    public void clear() {
+        internalMap.clear();
+    }
+
+
+    @Override
+    public V get(Object key) {
+        LinkedList<V> valueList = internalMap.get(key);
+
+        if (valueList != null)
+            return valueList.getLast();
+        else
+            return null;
+    }
+
+    /**
+     * @return a list of all values associated with the specified key. A empty list will be returned if the key does not exist.
+     */
+    public List<V> getAll(Object key) {
+        LinkedList<V> valueList = internalMap.get(key);
+
+        if (valueList != null)
+            return Collections.unmodifiableList(valueList);
+        else
+            return Collections.emptyList();
+    }
+
+    @Override
+    public Set<K> keySet() {
+        return internalMap.keySet();
+    }
+
+    @Override
+    public Collection<V> values() {
+        LinkedList<V> list = new LinkedList<>();
+
+        for(List<V> valueList : internalMap.values()) {
+            list.addAll(valueList);
+        }
+
+        return list;
+    }
+
+    @Override
+    public Set<Entry<K, V>> entrySet() {
+        throw new UnsupportedOperationException();
+    }
+
+
+}