com.aliyun.openservices.eas.discovery.utils.CollectionUtils Maven / Gradle / Ivy
package com.aliyun.openservices.eas.discovery.utils;
/**
* Created by harold on 2015/12/7.
*/
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.util.*;
/**
* Provides utility methods and decorators for {@link Collection} instances.
*
* @author Rodney Waldhoff
* @author Paul Jack
* @author Stephen Colebourne
* @author Steve Downey
* @author Herve Quiroz
* @author Peter KoBek
* @author Matthew Hawthorne
* @author Janek Bogucki
* @author Phil Steitz
* @author Steven Melzer
* @author Jon Schewe
* @author Neil O'Toole
* @author Stephen Smith
* @version $Revision: 1713167 $ $Date: 2015-11-07 20:44:03 +0100 (Sat, 07 Nov 2015) $
* @since Commons Collections 1.0
*/
public class CollectionUtils {
/**
* Constant to avoid repeated object creation
*/
private static Integer INTEGER_ONE = new Integer(1);
/**
* CollectionUtils should not normally be instantiated.
*/
public CollectionUtils() {
}
public static Collection subtract(final Collection a, final Collection b) {
ArrayList list = new ArrayList(a);
for (Iterator it = b.iterator(); it.hasNext(); ) {
list.remove(it.next());
}
return list;
}
/**
* Returns a {@link Map} mapping each unique element in the given
* {@link Collection} to an {@link Integer} representing the number
* of occurrences of that element in the {@link Collection}.
*
* Only those elements present in the collection will appear as
* keys in the map.
*
* @param coll the collection to get the cardinality map for, must not be null
* @return the populated cardinality map
*/
public static Map getCardinalityMap(final Collection coll) {
Map count = new HashMap();
for (Iterator it = coll.iterator(); it.hasNext(); ) {
Object obj = it.next();
Integer c = (Integer) (count.get(obj));
if (c == null) {
count.put(obj, INTEGER_ONE);
} else {
count.put(obj, new Integer(c.intValue() + 1));
}
}
return count;
}
public static boolean isEqualCollection(final Collection a, final Collection b) {
if (a.size() != b.size()) {
return false;
} else {
Map mapa = getCardinalityMap(a);
Map mapb = getCardinalityMap(b);
if (mapa.size() != mapb.size()) {
return false;
} else {
Iterator it = mapa.keySet().iterator();
while (it.hasNext()) {
Object obj = it.next();
if (getFreq(obj, mapa) != getFreq(obj, mapb)) {
return false;
}
}
return true;
}
}
}
//-----------------------------------------------------------------------
/**
* Null-safe check if the specified collection is empty.
*
* Null returns true.
*
* @param coll the collection to check, may be null
* @return true if empty or null
* @since Commons Collections 3.2
*/
public static boolean isEmpty(Collection coll) {
return (coll == null || coll.isEmpty());
}
private static final int getFreq(final Object obj, final Map freqMap) {
Integer count = (Integer) freqMap.get(obj);
if (count != null) {
return count.intValue();
}
return 0;
}
}