Add some common collection filters.

diff --git a/src/net/pterodactylus/util/filter/Filters.java b/src/net/pterodactylus/util/filter/Filters.java
new file mode 100644 (file)
index 0000000..fe3f12f
--- /dev/null
+++ b/src/net/pterodactylus/util/filter/Filters.java
@@ -0,0 +1,191 @@
+/*
+ * jFCPlib - Filters.java -
+ * Copyright © 2009 David Roden
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ */
+package net.pterodactylus.util.filter;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.Set;
+import java.util.Map.Entry;
+
+/**
+ * Defines various methods to filter {@link Collection}s.
+ *
+ * @author David ‘Bombe’ Roden <bombe@freenetproject.org>
+ */
+public class Filters {
+
+       /**
+        * Returns a list that contains only the elements from the given list that
+        * match the given filter.
+        *
+        * @param <E>
+        *            The type of the list elements
+        * @param list
+        *            The list to filter
+        * @param listFilter
+        *            The list filter
+        * @return The filtered list
+        */
+       public static <E> List<E> filteredList(List<E> list, Filter<E> listFilter) {
+               List<E> filteredList = new ArrayList<E>();
+               for (E element : list) {
+                       if (listFilter.filterObject(element)) {
+                               filteredList.add(element);
+                       }
+               }
+               return filteredList;
+       }
+
+       /**
+        * Returns a set that contains only the elements from the given set that
+        * match the given filter.
+        *
+        * @param <E>
+        *            The type of the set elements
+        * @param set
+        *            The set to filter
+        * @param setFilter
+        *            The set filter
+        * @return The filtered set
+        */
+       public static <E> Set<E> filteredSet(Set<E> set, Filter<E> setFilter) {
+               Set<E> filteredSet = new HashSet<E>();
+               for (E element : set) {
+                       if (setFilter.filterObject(element)) {
+                               filteredSet.add(element);
+                       }
+               }
+               return filteredSet;
+       }
+
+       /**
+        * Returns a map that contains only the elements from the given map that
+        * match the given filter.
+        *
+        * @param <K>
+        *            The type of the map keys
+        * @param <V>
+        *            The type of the map values
+        * @param map
+        *            The map to filter
+        * @param mapFilter
+        *            The map filter
+        * @return The filtered map
+        */
+       public static <K, V> Map<K, V> filteredMap(Map<K, V> map, Filter<Entry<K, V>> mapFilter) {
+               Map<K, V> filteredMap = new HashMap<K, V>();
+               for (Entry<K, V> element : map.entrySet()) {
+                       if (mapFilter.filterObject(element)) {
+                               filteredMap.put(element.getKey(), element.getValue());
+                       }
+               }
+               return filteredMap;
+       }
+
+       /**
+        * Returns a collection that contains only the elements from the given
+        * collection that match the given filter.
+        *
+        * @param <K>
+        *            The type of the collection values
+        * @param collection
+        *            The collection to filter
+        * @param collectionFilter
+        *            The collection filter
+        * @return The filtered collection
+        */
+       public static <K> Collection<K> filteredCollection(Collection<K> collection, Filter<K> collectionFilter) {
+               return filteredList(new ArrayList<K>(collection), collectionFilter);
+       }
+
+       /**
+        * Returns an iterator that contains only the elements from the given
+        * iterator that match the given filter.
+        *
+        * @param <E>
+        *            The type of the iterator elements
+        * @param iterator
+        *            The iterator to filter
+        * @param iteratorFilter
+        *            The iterator filter
+        * @return The filtered iterator
+        */
+       public static <E> Iterator<E> filteredIterator(final Iterator<E> iterator, final Filter<E> iteratorFilter) {
+               return new Iterator<E>() {
+
+                       private boolean gotNextElement = false;
+
+                       private E nextElement;
+
+                       private void getNextElement() {
+                               if (gotNextElement) {
+                                       return;
+                               }
+                               while (iterator.hasNext()) {
+                                       nextElement = iterator.next();
+                                       if (iteratorFilter.filterObject(nextElement)) {
+                                               gotNextElement = true;
+                                               break;
+                                       }
+                               }
+                       }
+
+                       /**
+                        * {@inheritDoc}
+                        *
+                        * @see java.util.Iterator#hasNext()
+                        */
+                       public boolean hasNext() {
+                               getNextElement();
+                               return gotNextElement;
+                       }
+
+                       /**
+                        * {@inheritDoc}
+                        *
+                        * @see java.util.Iterator#next()
+                        */
+                       public E next() {
+                               getNextElement();
+                               if (!gotNextElement) {
+                                       throw new NoSuchElementException("no more elements in iteration");
+                               }
+                               gotNextElement = false;
+                               return nextElement;
+                       }
+
+                       /**
+                        * {@inheritDoc}
+                        *
+                        * @see java.util.Iterator#remove()
+                        */
+                       public void remove() {
+                               throw new UnsupportedOperationException("remove() not supported on this iteration");
+                       }
+
+               };
+       }
+
+}