Java List Intersect intersect(List<? extends T> list1, List<? extends T> list2)

Description

This method returns a new ArrayList which is the intersection of the two List parameters, based on Object#equals(Object) equality of their elements.

License

Open Source License

Return

a new ArrayList whose values represent the intersection of the two Lists.

Declaration

public static <T> List<T> intersect(List<? extends T> list1, List<? extends T> list2)

Method Source Code

//package com.java2s;
/*/*from   w w w  .j a  va  2s . co m*/
 * Copyright (C) 2005-2014 Alfresco Software Limited.
 *
 * This file is part of Alfresco
 *
 * Alfresco is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Alfresco 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with Alfresco. If not, see <http://www.gnu.org/licenses/>.
 */

import java.util.ArrayList;

import java.util.Collection;
import java.util.Collections;

import java.util.HashMap;
import java.util.HashSet;

import java.util.List;
import java.util.Map;

import java.util.Set;

public class Main {
    /**
     * This method returns a new ArrayList which is the intersection of the two List parameters, based on {@link Object#equals(Object) equality}
     * of their elements.
     * The intersection list will contain elements in the order they have in list1 and any references in the resultant list will be
     * to elements within list1 also.
     * 
     * @return a new ArrayList whose values represent the intersection of the two Lists.
     */
    public static <T> List<T> intersect(List<? extends T> list1, List<? extends T> list2) {
        if (list1 == null || list1.isEmpty() || list2 == null || list2.isEmpty()) {
            return Collections.emptyList();
        }

        List<T> result = new ArrayList<T>();
        result.addAll(list1);

        result.retainAll(list2);

        return result;
    }

    /**
     * This method returns a new HashMap which is the intersection of the two Map parameters, based on {@link Object#equals(Object) equality}
     * of their entries.
     * Any references in the resultant map will be to elements within map1.
     * 
     * @return a new HashMap whose values represent the intersection of the two Maps.
     */
    public static <K, V> Map<K, V> intersect(Map<K, V> map1, Map<K, V> map2) {
        if (map1 == null || map1.isEmpty() || map2 == null || map2.isEmpty()) {
            return Collections.emptyMap();
        }

        // We now know neither map is null.
        Map<K, V> result = new HashMap<K, V>();
        for (Map.Entry<K, V> item : map1.entrySet()) {
            V value = map2.get(item.getKey());
            if (value != null && value.equals(item.getValue())) {
                result.put(item.getKey(), item.getValue());
            }
        }

        return result;
    }

    /**
     * This method returns a new HashSet which is the intersection of the two Set parameters, based on {@link Object#equals(Object) equality}
     * of their elements.
     * Any references in the resultant set will be to elements within set1.
     * 
     * @return a new HashSet whose values represent the intersection of the two Sets.
     */
    public static <T> Set<T> intersect(Set<? extends T> set1, Set<? extends T> set2) {
        if (set1 == null || set1.isEmpty() || set2 == null || set2.isEmpty()) {
            return Collections.emptySet();
        }

        Set<T> result = new HashSet<T>();
        result.addAll(set1);

        result.retainAll(set2);

        return result;
    }

    public static boolean isEmpty(Map<?, ?> map) {
        if (map == null) {
            return true;
        }
        return map.isEmpty();
    }

    public static boolean isEmpty(Collection<?> items) {
        if (items == null) {
            return true;
        }
        return items.isEmpty();
    }
}

Java List Intersect intersect(List list1, List list2)

Description

License

Return

Declaration

Method Source Code

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