001    /*
002     * Created on Nov 1, 2007
003     *
004     * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
005     * the License. You may obtain a copy of the License at
006     *
007     * http://www.apache.org/licenses/LICENSE-2.0
008     *
009     * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
010     * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
011     * specific language governing permissions and limitations under the License.
012     *
013     * Copyright @2007-2011 the original author or authors.
014     */
015    package org.fest.util;
016    
017    import java.util.*;
018    
019    /**
020     * Filters elements of a collection by their data type.
021     * @param <T> the generic type of the objects returned by the filter.
022     *
023     * @author Yvonne Wang
024     */
025    public class TypeFilter<T> implements CollectionFilter<T> {
026    
027      /**
028       * Creates a new <code>{@link TypeFilter}</code>.
029       * @param <T> the generic type of the target type.
030       * @param type the target type for this filter.
031       * @return the created filter.
032       */
033      public static <T> TypeFilter<T> byType(Class<T> type) {
034        return new TypeFilter<T>(type);
035      }
036    
037      private final Class<T> type;
038    
039      TypeFilter(Class<T> type) {
040        this.type = type;
041      }
042    
043      /**
044       * Filters the given collection by the type specified in this filter.
045       * @param target the collection to filter.
046       * @return a list containing the filtered elements.
047       * @throws IllegalArgumentException if the given collection is {@code null}.
048       */
049      @SuppressWarnings("unchecked") public List<T> filter(Collection<?> target) {
050        if (target == null) throw new IllegalArgumentException("The collection to filter should not be null");
051        List<Object> filtered = new ArrayList<Object>();
052        for (Object o : target) {
053          if (o == null) continue;
054          if (type.isAssignableFrom(o.getClass())) filtered.add(o);
055        }
056        return (List<T>) filtered;
057      }
058    }