com.alibaba.nacos.client.naming.utils.CollectionUtils Maven / Gradle / Ivy
/*
* Copyright 1999-2018 Alibaba Group Holding Ltd.
*
* Licensed 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.
*/
package com.alibaba.nacos.client.naming.utils;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
/**
* 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 final Integer INTEGER_ONE = 1;
/**
* Returns a new {@link Collection} containing a - b. The cardinality of each element
* e in the returned {@link Collection} will be the cardinality of e in a minus the
* cardinality of e in b, or zero, whichever is greater.
*
* @param a the collection to subtract from, must not be null
* @param b the collection to subtract, must not be null
* @return a new collection with the results
* @see Collection#removeAll
*/
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(coll.size());
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, c + 1);
}
}
return count;
}
/**
* Returns true iff the given {@link Collection}s contain exactly the same elements with exactly the same
* cardinalities.
*
*
That is, iff the cardinality of e in a is equal to the cardinality of e in b, for
* each element e in a or b.
*
* @param a the first collection, must not be null
* @param b the second collection, must not be null
* @return true iff the collections contain the same elements with the same cardinalities.
*/
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 int getFreq(final Object obj, final Map freqMap) {
Integer count = (Integer) freqMap.get(obj);
if (count != null) {
return count.intValue();
}
return 0;
}
}