org.compass.core.util.CollectionUtils Maven / Gradle / Ivy
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/*
* Copyright 2004-2009 the original author or authors.
*
* 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 org.compass.core.util;
import java.util.Arrays;
import java.util.Collection;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Properties;
/**
* A set of collection based utilities.
*
* @author kimchy
*/
public abstract class CollectionUtils {
public static int absHash(Object obj) {
return Math.abs(hash(obj));
}
/**
* Same hash function as HashMap#newHash method.
*/
public static int hash(Object obj) {
int h = obj.hashCode();
// This function ensures that hashCodes that differ only by
// constant multiples at each bit position have a bounded
// number of collisions (approximately 8 at default load factor).
h ^= (h >>> 20) ^ (h >>> 12);
return h ^ (h >>> 7) ^ (h >>> 4);
}
/**
* Return true if the supplied Collection is null
* or empty. Otherwise, return false.
*
* @param collection the Collection to check
* @return whether the given Collection is empty
*/
public static boolean isEmpty(Collection collection) {
return (collection == null || collection.isEmpty());
}
/**
* Return true if the supplied Map is null
* or empty. Otherwise, return false.
*
* @param map the Map to check
* @return whether the given Map is empty
*/
public static boolean isEmpty(Map map) {
return (map == null || map.isEmpty());
}
/**
* Convert the supplied array into a List. A primitive array gets
* converted into a List of the appropriate wrapper type.
* A null source value will be converted to an
* empty List.
*
* @param source the (potentially primitive) array
* @return the converted List result
* @see ObjectUtils#toObjectArray(Object)
*/
public static List arrayToList(Object source) {
return Arrays.asList(ObjectUtils.toObjectArray(source));
}
/**
* Merge the given array into the given Collection.
*
* @param array the array to merge (may be null)
* @param collection the target Collection to merge the array into
*/
public static void mergeArrayIntoCollection(Object array, Collection collection) {
if (collection == null) {
throw new IllegalArgumentException("Collection must not be null");
}
Object[] arr = ObjectUtils.toObjectArray(array);
for (int i = 0; i < arr.length; i++) {
collection.add(arr[i]);
}
}
/**
* Merge the given Properties instance into the given Map,
* copying all properties (key-value pairs) over.
*
Uses Properties.propertyNames() to even catch
* default properties linked into the original Properties instance.
*
* @param props the Properties instance to merge (may be null)
* @param map the target Map to merge the properties into
*/
public static void mergePropertiesIntoMap(Properties props, Map map) {
if (map == null) {
throw new IllegalArgumentException("Map must not be null");
}
if (props != null) {
for (Enumeration en = props.propertyNames(); en.hasMoreElements();) {
String key = (String) en.nextElement();
map.put(key, props.getProperty(key));
}
}
}
/**
* Check whether the given Iterator contains the given element.
*
* @param iterator the Iterator to check
* @param element the element to look for
* @return true if found, false else
*/
public static boolean contains(Iterator iterator, Object element) {
if (iterator != null) {
while (iterator.hasNext()) {
Object candidate = iterator.next();
if (ObjectUtils.nullSafeEquals(candidate, element)) {
return true;
}
}
}
return false;
}
/**
* Check whether the given Enumeration contains the given element.
*
* @param enumeration the Enumeration to check
* @param element the element to look for
* @return true if found, false else
*/
public static boolean contains(Enumeration enumeration, Object element) {
if (enumeration != null) {
while (enumeration.hasMoreElements()) {
Object candidate = enumeration.nextElement();
if (ObjectUtils.nullSafeEquals(candidate, element)) {
return true;
}
}
}
return false;
}
/**
* Check whether the given Collection contains the given element instance.
*
Enforces the given instance to be present, rather than returning
* true for an equal element as well.
*
* @param collection the Collection to check
* @param element the element to look for
* @return true if found, false else
*/
public static boolean containsInstance(Collection collection, Object element) {
if (collection != null) {
for (Object candidate : collection) {
if (candidate == element) {
return true;
}
}
}
return false;
}
/**
* Return true if any element in 'candidates' is
* contained in 'source'; otherwise returns false.
*
* @param source the source Collection
* @param candidates the candidates to search for
* @return whether any of the candidates has been found
*/
public static boolean containsAny(Collection source, Collection candidates) {
if (isEmpty(source) || isEmpty(candidates)) {
return false;
}
for (Object candidate : candidates) {
if (source.contains(candidate)) {
return true;
}
}
return false;
}
/**
* Return the first element in 'candidates' that is contained in
* 'source'. If no element in 'candidates' is present in
* 'source' returns null. Iteration order is
* {@link Collection} implementation specific.
*
* @param source the source Collection
* @param candidates the candidates to search for
* @return the first present object, or null if not found
*/
public static Object findFirstMatch(Collection source, Collection candidates) {
if (isEmpty(source) || isEmpty(candidates)) {
return null;
}
for (Object candidate : candidates) {
if (source.contains(candidate)) {
return candidate;
}
}
return null;
}
/**
* Find a single value of the given type in the given Collection.
*
* @param collection the Collection to search
* @param type the type to look for
* @return a value of the given type found if there is a clear match,
* or null if none or more than one such value found
*/
public static Object findValueOfType(Collection collection, Class type) {
if (isEmpty(collection)) {
return null;
}
Object value = null;
for (Object obj : collection) {
if (type == null || type.isInstance(obj)) {
if (value != null) {
// More than one value found... no clear single value.
return null;
}
value = obj;
}
}
return value;
}
/**
* Find a single value of one of the given types in the given Collection:
* searching the Collection for a value of the first type, then
* searching for a value of the second type, etc.
*
* @param collection the collection to search
* @param types the types to look for, in prioritized order
* @return a value of one of the given types found if there is a clear match,
* or null if none or more than one such value found
*/
public static Object findValueOfType(Collection collection, Class[] types) {
if (isEmpty(collection) || ObjectUtils.isEmpty(types)) {
return null;
}
for (Class type : types) {
Object value = findValueOfType(collection, type);
if (value != null) {
return value;
}
}
return null;
}
/**
* Determine whether the given Collection only contains a single unique object.
*
* @param collection the Collection to check
* @return true if the collection contains a single reference or
* multiple references to the same instance, false else
*/
public static boolean hasUniqueObject(Collection collection) {
if (isEmpty(collection)) {
return false;
}
boolean hasCandidate = false;
Object candidate = null;
for (Object elem : collection) {
if (!hasCandidate) {
hasCandidate = true;
candidate = elem;
} else if (candidate != elem) {
return false;
}
}
return true;
}
}