/*
* Copyright 2001-2005 The Apache Software Foundation
*
* 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.apache.commons.collections;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.Set;
import org.apache.commons.collections.collection.PredicatedCollection;
import org.apache.commons.collections.collection.SynchronizedCollection;
import org.apache.commons.collections.collection.TransformedCollection;
import org.apache.commons.collections.collection.TypedCollection;
import org.apache.commons.collections.collection.UnmodifiableBoundedCollection;
import org.apache.commons.collections.collection.UnmodifiableCollection;
/**
* Provides utility methods and decorators for {@link Collection} instances.
*
* @since Commons Collections 1.0
* @version $Revision: 348013 $ $Date: 2005-11-21 23:24:45 +0000 (Mon, 21 Nov 2005) $
*
* @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
*/
public class CollectionUtils {
/** Constant to avoid repeated object creation */
private static Integer INTEGER_ONE = new Integer(1);
/**
* An empty unmodifiable collection.
* The JDK provides empty Set and List implementations which could be used for
* this purpose. However they could be cast to Set or List which might be
* undesirable. This implementation only implements Collection.
*/
public static final Collection EMPTY_COLLECTION = UnmodifiableCollection.decorate(new ArrayList());
/**
* <code>CollectionUtils</code> should not normally be instantiated.
*/
public CollectionUtils() {
}
/**
* Returns a {@link Collection} containing the union
* of the given {@link Collection}s.
* <p>
* The cardinality of each element in the returned {@link Collection}
* will be equal to the maximum of the cardinality of that element
* in the two given {@link Collection}s.
*
* @param a the first collection, must not be null
* @param b the second collection, must not be null
* @return the union of the two collections
* @see Collection#addAll
*/
public static Collection union(final Collection a, final Collection b) {
ArrayList list = new ArrayList();
Map mapa = getCardinalityMap(a);
Map mapb = getCardinalityMap(b);
Set elts = new HashSet(a);
elts.addAll(b);
Iterator it = elts.iterator();
while(it.hasNext()) {
Object obj = it.next();
for(int i=0,m=Math.max(getFreq(obj,mapa),getFreq(obj,mapb));i<m;i++) {
list.add(obj);
}
}
return list;
}
/**
* Returns a {@link Collection} containing the intersection
* of the given {@link Collection}s.
* <p>
* The cardinality of each element in the returned {@link Collection}
* will be equal to the minimum of the cardinality of that element
* in the two given {@link Collection}s.
*
* @param a the first collection, must not be null
* @param b the second collection, must not be null
* @return the intersection of the two collections
* @see Collection#retainAll
* @see #containsAny
*/
public static Collection intersection(final Collection a, final Collection b) {
ArrayList list = new ArrayList();
Map mapa = getCardinalityMap(a);
Map mapb = getCardinalityMap(b);
Set elts = new HashSet(a);
elts.addAll(b);
Iterator it = elts.iterator();
while(it.hasNext()) {
Object obj = it.next();
for(int i=0,m=Math.min(getFreq(obj,mapa),getFreq(obj,mapb));i<m;i++) {
list.add(obj);
}
}
return list;
}
/**
* Returns a {@link Collection} containing the exclusive disjunction
* (symmetric difference) of the given {@link Collection}s.
* <p>
* The cardinality of each element <i>e</i> in the returned {@link Collection}
* will be equal to
* <tt>max(cardinality(<i>e</i>,<i>a</i>),cardinality(<i>e</i>,<i>b</i>)) - min(cardinality(<i>e</i>,<i>a</i>),cardinality(<i>e</i>,<i>b</i>))</tt>.
* <p>
* This is equivalent to
* <tt>{@link #subtract subtract}({@link #union union(a,b)},{@link #intersection intersection(a,b)})</tt>
* or
* <tt>{@link #union union}({@link #subtract subtract(a,b)},{@link #subtract subtract(b,a)})</tt>.
*
* @param a the first collection, must not be null
* @param b the second collection, must not be null
* @return the symmetric difference of the two collections
*/
public static Collection disjunction(final Collection a, final Collection b) {
ArrayList list = new ArrayList();
Map mapa = getCardinalityMap(a);
Map mapb = getCardinalityMap(b);
Set elts = new HashSet(a);
elts.addAll(b);
Iterator it = elts.iterator();
while(it.hasNext()) {
Object obj = it.next();
for(int i=0,m=((Math.max(getFreq(obj,mapa),getFreq(obj,mapb)))-(Math.min(getFreq(obj,mapa),getFreq(obj,mapb))));i<m;i++) {
list.add(obj);
}
}
return list;
}
/**
* Returns a new {@link Collection} containing <tt><i>a</i> - <i>b</i></tt>.
* The cardinality of each element <i>e</i> in the returned {@link Collection}
* will be the cardinality of <i>e</i> in <i>a</i> minus the cardinality
* of <i>e</i> in <i>b</i>, 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 <code>true</code> iff at least one element is in both collections.
* <p>
* In other words, this method returns <code>true</code> iff the
* {@link #intersection} of <i>coll1</i> and <i>coll2</i> is not empty.
*
* @param coll1 the first collection, must not be null
* @param coll2 the first collection, must not be null
* @return <code>true</code> iff the intersection of the collections is non-empty
* @since 2.1
* @see #intersection
*/
public static boolean containsAny(final Collection coll1, final Collection coll2) {
if (coll1.size() < coll2.size()) {
for (Iterator it = coll1.iterator(); it.hasNext();) {
if (coll2.contains(it.next())) {
return true;
}
}
} else {
for (Iterator it = coll2.iterator(); it.hasNext();) {
if (coll1.contains(it.next())) {
return true;
}
}
}
return false;
}
/**
* 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}.
* <p>
* 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;
}
/**
* Returns <tt>true</tt> iff <i>a</i> is a sub-collection of <i>b</i>,
* that is, iff the cardinality of <i>e</i> in <i>a</i> is less
* than or equal to the cardinality of <i>e</i> in <i>b</i>,
* for each element <i>e</i> in <i>a</i>.
*
* @param a the first (sub?) collection, must not be null
* @param b the second (super?) collection, must not be null
* @return <code>true</code> iff <i>a</i> is a sub-collection of <i>b</i>
* @see #isProperSubCollection
* @see Collection#containsAll
*/
public static boolean isSubCollection(final Collection a, final Collection b) {
Map mapa = getCardinalityMap(a);
Map mapb = getCardinalityMap(b);
Iterator it = a.iterator();
while (it.hasNext()) {
Object obj = it.next();
if (getFreq(obj, mapa) > getFreq(obj, mapb)) {
return false;
}
}
return true;
}
/**
* Returns <tt>true</tt> iff <i>a</i> is a <i>proper</i> sub-collection of <i>b</i>,
* that is, iff the cardinality of <i>e</i> in <i>a</i> is less
* than or equal to the cardinality of <i>e</i> in <i>b</i>,
* for each element <i>e</i> in <i>a</i>, and there is at least one
* element <i>f</i> such that the cardinality of <i>f</i> in <i>b</i>
* is strictly greater than the cardinality of <i>f</i> in <i>a</i>.
* <p>
* The implementation assumes
* <ul>
* <li><code>a.size()</code> and <code>b.size()</code> represent the
* total cardinality of <i>a</i> and <i>b</i>, resp. </li>
* <li><code>a.size() < Integer.MAXVALUE</code></li>
* </ul>
*
* @param a the first (sub?) collection, must not be null
* @param b the second (super?) collection, must not be null
* @return <code>true</code> iff <i>a</i> is a <i>proper</i> sub-collection of <i>b</i>
* @see #isSubCollection
* @see Collection#containsAll
*/
public static boolean isProperSubCollection(final Collection a, final Collection b) {
return (a.size() < b.size()) && CollectionUtils.isSubCollection(a,b);
}
/**
* Returns <tt>true</tt> iff the given {@link Collection}s contain
* exactly the same elements with exactly the same cardinalities.
* <p>
* That is, iff the cardinality of <i>e</i> in <i>a</i> is
* equal to the cardinality of <i>e</i> in <i>b</i>,
* for each element <i>e</i> in <i>a</i> or <i>b</i>.
*
* @param a the first collection, must not be null
* @param b the second collection, must not be null
* @return <code>true</code> 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;
}
}
}
/**
* Returns the number of occurrences of <i>obj</i> in <i>coll</i>.
*
* @param obj the object to find the cardinality of
* @param coll the collection to search
* @return the the number of occurrences of obj in coll
*/
public static int cardinality(Object obj, final Collection coll) {
if (coll instanceof Set) {
return (coll.contains(obj) ? 1 : 0);
}
if (coll instanceof Bag) {
return ((Bag) coll).getCount(obj);
}
int count = 0;
if (obj == null) {
for (Iterator it = coll.iterator();it.hasNext();) {
if (it.next() == null) {
count++;
}
}
} else {
for (Iterator it = coll.iterator();it.hasNext();) {
if (obj.equals(it.next())) {
count++;
}
}
}
return count;
}
/**
* Finds the first element in the given collection which matches the given predicate.
* <p>
* If the input collection or predicate is null, or no element of the collection
* matches the predicate, null is returned.
*
* @param collection the collection to search, may be null
* @param predicate the predicate to use, may be null
* @return the first element of the collection which matches the predicate or null if none could be found
*/
public static Object find(Collection collection, Predicate predicate) {
if (collection != null && predicate != null) {
for (Iterator iter = collection.iterator(); iter.hasNext();) {
Object item = iter.next();
if (predicate.evaluate(item)) {
return item;
}
}
}
return null;
}
/**
* Executes the given closure on each element in the collection.
* <p>
* If the input collection or closure is null, there is no change made.
*
* @param collection the collection to get the input from, may be null
* @param closure the closure to perform, may be null
*/
public static void forAllDo(Collection collection, Closure closure) {
if (collection != null && closure != null) {
for (Iterator it = collection.iterator(); it.hasNext();) {
closure.execute(it.next());
}
}
}
/**
* Filter the collection by applying a Predicate to each element. If the
* predicate returns false, remove the element.
* <p>
* If the input collection or predicate is null, there is no change made.
*
* @param collection the collection to get the input from, may be null
* @param predicate the predicate to use as a filter, may be null
*/
public static void filter(Collection collection, Predicate predicate) {
if (collection != null && predicate != null) {
for (Iterator it = collection.iterator(); it.hasNext();) {
if (predicate.evaluate(it.next()) == false) {
it.remove();
}
}
}
}
/**
* Transform the collection by applying a Transformer to each element.
* <p>
* If the input collection or transformer is null, there is no change made.
* <p>
* This routine is best for Lists, for which set() is used to do the
* transformations "in place." For other Collections, clear() and addAll()
* are used to replace elements.
* <p>
* If the input collection controls its input, such as a Set, and the
* Transformer creates duplicates (or are otherwise invalid), the
* collection may reduce in size due to calling this method.
*
* @param collection the collection to get the input from, may be null
* @param transformer the transformer to perform, may be null
*/
public static void transform(Collection collection, Transformer transformer) {
if (collection != null && transformer != null) {
if (collection instanceof List) {
List list = (List) collection;
for (ListIterator it = list.listIterator(); it.hasNext();) {
it.set(transformer.transform(it.next()));
}
} else {
Collection resultCollection = collect(collection, transformer);
collection.clear();
collection.addAll(resultCollection);
}
}
}
/**
* Counts the number of elements in the input collection that match the predicate.
* <p>
* A <code>null</code> collection or predicate matches no elements.
*
* @param inputCollection the collection to get the input from, may be null
* @param predicate the predicate to use, may be null
* @return the number of matches for the predicate in the collection
*/
public static int countMatches(Collection inputCollection, Predicate predicate) {
int count = 0;
if (inputCollection != null && predicate != null) {
for (Iterator it = inputCollection.iterator(); it.hasNext();) {
if (predicate.evaluate(it.next())) {
count++;
}
}
}
return count;
}
/**
* Answers true if a predicate is true for at least one element of a collection.
* <p>
* A <code>null</code> collection or predicate returns false.
*
* @param collection the collection to get the input from, may be null
* @param predicate the predicate to use, may be null
* @return true if at least one element of the collection matches the predicate
*/
public static boolean exists(Collection collection, Predicate predicate) {
if (collection != null && predicate != null) {
for (Iterator it = collection.iterator(); it.hasNext();) {
if (predicate.evaluate(it.next())) {
return true;
}
}
}
return false;
}
/**
* Selects all elements from input collection which match the given predicate
* into an output collection.
* <p>
* A <code>null</code> predicate matches no elements.
*
* @param inputCollection the collection to get the input from, may not be null
* @param predicate the predicate to use, may be null
* @return the elements matching the predicate (new list)
* @throws NullPointerException if the input collection is null
*/
public static Collection select(Collection inputCollection, Predicate predicate) {
ArrayList answer = new ArrayList(inputCollection.size());
select(inputCollection, predicate, answer);
return answer;
}
/**
* Selects all elements from input collection which match the given predicate
* and adds them to outputCollection.
* <p>
* If the input collection or predicate is null, there is no change to the
* output collection.
*
* @param inputCollection the collection to get the input from, may be null
* @param predicate the predicate to use, may be null
* @param outputCollection the collection to output into, may not be null
*/
public static void select(Collection inputCollection, Predicate predicate, Collection outputCollection) {
if (inputCollection != null && predicate != null) {
for (Iterator iter = inputCollection.iterator(); iter.hasNext();) {
Object item = iter.next();
if (predicate.evaluate(item)) {
outputCollection.add(item);
}
}
}
}
/**
* Selects all elements from inputCollection which don't match the given predicate
* into an output collection.
* <p>
* If the input predicate is <code>null</code>, the result is an empty list.
*
* @param inputCollection the collection to get the input from, may not be null
* @param predicate the predicate to use, may be null
* @return the elements <b>not</b> matching the predicate (new list)
* @throws NullPointerException if the input collection is null
*/
public static Collection selectRejected(Collection inputCollection, Predicate predicate) {
ArrayList answer = new ArrayList(inputCollection.size());
selectRejected(inputCollection, predicate, answer);
return answer;
}
/**
* Selects all elements from inputCollection which don't match the given predicate
* and adds them to outputCollection.
* <p>
* If the input predicate is <code>null</code>, no elements are added to <code>outputCollection</code>.
*
* @param inputCollection the collection to get the input from, may be null
* @param predicate the predicate to use, may be null
* @param outputCollection the collection to output into, may not be null
*/
public static void selectRejected(Collection inputCollection, Predicate predicate, Collection outputCollection) {
if (inputCollection != null && predicate != null) {
for (Iterator iter = inputCollection.iterator(); iter.hasNext();) {
Object item = iter.next();
if (predicate.evaluate(item) == false) {
outputCollection.add(item);
}
}
}
}
/**
* Returns a new Collection consisting of the elements of inputCollection transformed
* by the given transformer.
* <p>
* If the input transformer is null, the result is an empty list.
*
* @param inputCollection the collection to get the input from, may not be null
* @param transformer the transformer to use, may be null
* @return the transformed result (new list)
* @throws NullPointerException if the input collection is null
*/
public static Collection collect(Collection inputCollection, Transformer transformer) {
ArrayList answer = new ArrayList(inputCollection.size());
collect(inputCollection, transformer, answer);
return answer;
}
/**
* Transforms all elements from the inputIterator with the given transformer
* and adds them to the outputCollection.
* <p>
* If the input iterator or transformer is null, the result is an empty list.
*
* @param inputIterator the iterator to get the input from, may be null
* @param transformer the transformer to use, may be null
* @return the transformed result (new list)
*/
public static Collection collect(Iterator inputIterator, Transformer transformer) {
ArrayList answer = new ArrayList();
collect(inputIterator, transformer, answer);
return answer;
}
/**
* Transforms all elements from inputCollection with the given transformer
* and adds them to the outputCollection.
* <p>
* If the input collection or transformer is null, there is no change to the
* output collection.
*
* @param inputCollection the collection to get the input from, may be null
* @param transformer the transformer to use, may be null
* @param outputCollection the collection to output into, may not be null
* @return the outputCollection with the transformed input added
* @throws NullPointerException if the output collection is null
*/
public static Collection collect(Collection inputCollection, final Transformer transformer, final Collection outputCollection) {
if (inputCollection != null) {
return collect(inputCollection.iterator(), transformer, outputCollection);
}
return outputCollection;
}
/**
* Transforms all elements from the inputIterator with the given transformer
* and adds them to the outputCollection.
* <p>
* If the input iterator or transformer is null, there is no change to the
* output collection.
*
* @param inputIterator the iterator to get the input from, may be null
* @param transformer the transformer to use, may be null
* @param outputCollection the collection to output into, may not be null
* @return the outputCollection with the transformed input added
* @throws NullPointerException if the output collection is null
*/
public static Collection collect(Iterator inputIterator, final Transformer transformer, final Collection outputCollection) {
if (inputIterator != null && transformer != null) {
while (inputIterator.hasNext()) {
Object item = inputIterator.next();
Object value = transformer.transform(item);
outputCollection.add(value);
}
}
return outputCollection;
}
//-----------------------------------------------------------------------
/**
* Adds an element to the collection unless the element is null.
*
* @param collection the collection to add to, must not be null
* @param object the object to add, if null it will not be added
* @return true if the collection changed
* @throws NullPointerException if the collection is null
* @since Commons Collections 3.2
*/
public static boolean addIgnoreNull(Collection collection, Object object) {
return (object == null ? false : collection.add(object));
}
/**
* Adds all elements in the iteration to the given collection.
*
* @param collection the collection to add to, must not be null
* @param iterator the iterator of elements to add, must not be null
* @throws NullPointerException if the collection or iterator is null
*/
public static void addAll(Collection collection, Iterator iterator) {
while (iterator.hasNext()) {
collection.add(iterator.next());
}
}
/**
* Adds all elements in the enumeration to the given collection.
*
* @param collection the collection to add to, must not be null
* @param enumeration the enumeration of elements to add, must not be null
* @throws NullPointerException if the collection or enumeration is null
*/
public static void addAll(Collection collection, Enumeration enumeration) {
while (enumeration.hasMoreElements()) {
collection.add(enumeration.nextElement());
}
}
/**
* Adds all elements in the array to the given collection.
*
* @param collection the collection to add to, must not be null
* @param elements the array of elements to add, must not be null
* @throws NullPointerException if the collection or array is null
*/
public static void addAll(Collection collection, Object[] elements) {
for (int i = 0, size = elements.length; i < size; i++) {
collection.add(elements[i]);
}
}
/**
* Given an Object, and an index, returns the nth value in the
* object.
* <ul>
* <li>If obj is a Map, returns the nth value from the <b>keySet</b> iterator, unless
* the Map contains an Integer key with integer value = idx, in which case the
* corresponding map entry value is returned. If idx exceeds the number of entries in
* the map, an empty Iterator is returned.
* <li>If obj is a List or an array, returns the nth value, throwing IndexOutOfBoundsException,
* ArrayIndexOutOfBoundsException, resp. if the nth value does not exist.
* <li>If obj is an iterator, enumeration or Collection, returns the nth value from the iterator,
* returning an empty Iterator (resp. Enumeration) if the nth value does not exist.
* <li>Returns the original obj if it is null or not a Collection or Iterator.
* </ul>
*
* @param obj the object to get an index of, may be null
* @param idx the index to get
* @throws IndexOutOfBoundsException
* @throws ArrayIndexOutOfBoundsException
*
* @deprecated use {@link #get(Object, int)} instead. Will be removed in v4.0
*/
public static Object index(Object obj, int idx) {
return index(obj, new Integer(idx));
}
/**
* Given an Object, and a key (index), returns the value associated with
* that key in the Object. The following checks are made:
* <ul>
* <li>If obj is a Map, use the index as a key to get a value. If no match continue.
* <li>Check key is an Integer. If not, return the object passed in.
* <li>If obj is a Map, get the nth value from the <b>keySet</b> iterator.
* If the Map has fewer than n entries, return an empty Iterator.
* <li>If obj is a List or an array, get the nth value, throwing IndexOutOfBoundsException,
* ArrayIndexOutOfBoundsException, resp. if the nth value does not exist.
* <li>If obj is an iterator, enumeration or Collection, get the nth value from the iterator,
* returning an empty Iterator (resp. Enumeration) if the nth value does not exist.
* <li>Return the original obj.
* </ul>
*
* @param obj the object to get an index of
* @param index the index to get
* @return the object at the specified index
* @throws IndexOutOfBoundsException
* @throws ArrayIndexOutOfBoundsException
*
* @deprecated use {@link #get(Object, int)} instead. Will be removed in v4.0
*/
public static Object index(Object obj, Object index) {
if(obj instanceof Map) {
Map map = (Map)obj;
if(map.containsKey(index)) {
return map.get(index);
}
}
int idx = -1;
if(index instanceof Integer) {
idx = ((Integer)index).intValue();
}
if(idx < 0) {
return obj;
}
else if(obj instanceof Map) {
Map map = (Map)obj;
Iterator iterator = map.keySet().iterator();
return index(iterator, idx);
}
else if(obj instanceof List) {
return ((List)obj).get(idx);
}
else if(obj instanceof Object[]) {
return ((Object[])obj)[idx];
}
else if(obj instanceof Enumeration) {
Enumeration it = (Enumeration)obj;
while(it.hasMoreElements()) {
idx--;
if(idx == -1) {
return it.nextElement();
} else {
it.nextElement();
}
}
}
else if(obj instanceof Iterator) {
return index((Iterator)obj, idx);
}
else if(obj instanceof Collection) {
Iterator iterator = ((Collection)obj).iterator();
return index(iterator, idx);
}
return obj;
}
private static Object index(Iterator iterator, int idx) {
while(iterator.hasNext()) {
idx--;
if(idx == -1) {
return iterator.next();
} else {
iterator.next();
}
}
return iterator;
}
/**
* Returns the <code>index</code>-th value in <code>object</code>, throwing
* <code>IndexOutOfBoundsException</code> if there is no such element or
* <code>IllegalArgumentException</code> if <code>object</code> is not an
* instance of one of the supported types.
* <p>
* The supported types, and associated semantics are:
* <ul>
* <li> Map -- the value returned is the <code>Map.Entry</code> in position
* <code>index</code> in the map's <code>entrySet</code> iterator,
* if there is such an entry.</li>
* <li> List -- this method is equivalent to the list's get method.</li>
* <li> Array -- the <code>index</code>-th array entry is returned,
* if there is such an entry; otherwise an <code>IndexOutOfBoundsException</code>
* is thrown.</li>
* <li> Collection -- the value returned is the <code>index</code>-th object
* returned by the collection's default iterator, if there is such an element.</li>
* <li> Iterator or Enumeration -- the value returned is the
* <code>index</code>-th object in the Iterator/Enumeration, if there
* is such an element. The Iterator/Enumeration is advanced to
* <code>index</code> (or to the end, if <code>index</code> exceeds the
* number of entries) as a side effect of this method.</li>
* </ul>
*
* @param object the object to get a value from
* @param index the index to get
* @return the object at the specified index
* @throws IndexOutOfBoundsException if the index is invalid
* @throws IllegalArgumentException if the object type is invalid
*/
public static Object get(Object object, int index) {
if (index < 0) {
throw new IndexOutOfBoundsException("Index cannot be negative: " + index);
}
if (object instanceof Map) {
Map map = (Map) object;
Iterator iterator = map.entrySet().iterator();
return get(iterator, index);
} else if (object instanceof List) {
return ((List) object).get(index);
} else if (object instanceof Object[]) {
return ((Object[]) object)[index];
} else if (object instanceof Iterator) {
Iterator it = (Iterator) object;
while (it.hasNext()) {
index--;
if (index == -1) {
return it.next();
} else {
it.next();
}
}
throw new IndexOutOfBoundsException("Entry does not exist: " + index);
} else if (object instanceof Collection) {
Iterator iterator = ((Collection) object).iterator();
return get(iterator, index);
} else if (object instanceof Enumeration) {
Enumeration it = (Enumeration) object;
while (it.hasMoreElements()) {
index--;
if (index == -1) {
return it.nextElement();
} else {
it.nextElement();
}
}
throw new IndexOutOfBoundsException("Entry does not exist: " + index);
} else if (object == null) {
throw new IllegalArgumentException("Unsupported object type: null");
} else {
try {
return Array.get(object, index);
} catch (IllegalArgumentException ex) {
throw new IllegalArgumentException("Unsupported object type: " + object.getClass().getName());
}
}
}
/**
* Gets the size of the collection/iterator specified.
* <p>
* This method can handles objects as follows
* <ul>
* <li>Collection - the collection size
* <li>Map - the map size
* <li>Array - the array size
* <li>Iterator - the number of elements remaining in the iterator
* <li>Enumeration - the number of elements remaining in the enumeration
* </ul>
*
* @param object the object to get the size of
* @return the size of the specified collection
* @throws IllegalArgumentException thrown if object is not recognised or null
* @since Commons Collections 3.1
*/
public static int size(Object object) {
int total = 0;
if (object instanceof Map) {
total = ((Map) object).size();
} else if (object instanceof Collection) {
total = ((Collection) object).size();
} else if (object instanceof Object[]) {
total = ((Object[]) object).length;
} else if (object instanceof Iterator) {
Iterator it = (Iterator) object;
while (it.hasNext()) {
total++;
it.next();
}
} else if (object instanceof Enumeration) {
Enumeration it = (Enumeration) object;
while (it.hasMoreElements()) {
total++;
it.nextElement();
}
} else if (object == null) {
throw new IllegalArgumentException("Unsupported object type: null");
} else {
try {
total = Array.getLength(object);
} catch (IllegalArgumentException ex) {
throw new IllegalArgumentException("Unsupported object type: " + object.getClass().getName());
}
}
return total;
}
/**
* Checks if the specified collection/array/iterator is empty.
* <p>
* This method can handles objects as follows
* <ul>
* <li>Collection - via collection isEmpty
* <li>Map - via map isEmpty
* <li>Array - using array size
* <li>Iterator - via hasNext
* <li>Enumeration - via hasMoreElements
* </ul>
* <p>
* Note: This method is named to avoid clashing with
* {@link #isEmpty(Collection)}.
*
* @param object the object to get the size of, not null
* @return true if empty
* @throws IllegalArgumentException thrown if object is not recognised or null
* @since Commons Collections 3.2
*/
public static boolean sizeIsEmpty(Object object) {
if (object instanceof Collection) {
return ((Collection) object).isEmpty();
} else if (object instanceof Map) {
return ((Map) object).isEmpty();
} else if (object instanceof Object[]) {
return ((Object[]) object).length == 0;
} else if (object instanceof Iterator) {
return ((Iterator) object).hasNext() == false;
} else if (object instanceof Enumeration) {
return ((Enumeration) object).hasMoreElements() == false;
} else if (object == null) {
throw new IllegalArgumentException("Unsupported object type: null");
} else {
try {
return Array.getLength(object) == 0;
} catch (IllegalArgumentException ex) {
throw new IllegalArgumentException("Unsupported object type: " + object.getClass().getName());
}
}
}
//-----------------------------------------------------------------------
/**
* Null-safe check if the specified collection is empty.
* <p>
* 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());
}
/**
* Null-safe check if the specified collection is not empty.
* <p>
* Null returns false.
*
* @param coll the collection to check, may be null
* @return true if non-null and non-empty
* @since Commons Collections 3.2
*/
public static boolean isNotEmpty(Collection coll) {
return !CollectionUtils.isEmpty(coll);
}
//-----------------------------------------------------------------------
/**
* Reverses the order of the given array.
*
* @param array the array to reverse
*/
public static void reverseArray(Object[] array) {
int i = 0;
int j = array.length - 1;
Object tmp;
while (j > i) {
tmp = array[j];
array[j] = array[i];
array[i] = tmp;
j--;
i++;
}
}
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;
}
/**
* Returns true if no more elements can be added to the Collection.
* <p>
* This method uses the {@link BoundedCollection} interface to determine the
* full status. If the collection does not implement this interface then
* false is returned.
* <p>
* The collection does not have to implement this interface directly.
* If the collection has been decorated using the decorators subpackage
* then these will be removed to access the BoundedCollection.
*
* @param coll the collection to check
* @return true if the BoundedCollection is full
* @throws NullPointerException if the collection is null
*/
public static boolean isFull(Collection coll) {
if (coll == null) {
throw new NullPointerException("The collection must not be null");
}
if (coll instanceof BoundedCollection) {
return ((BoundedCollection) coll).isFull();
}
try {
BoundedCollection bcoll = UnmodifiableBoundedCollection.decorateUsing(coll);
return bcoll.isFull();
} catch (IllegalArgumentException ex) {
return false;
}
}
/**
* Get the maximum number of elements that the Collection can contain.
* <p>
* This method uses the {@link BoundedCollection} interface to determine the
* maximum size. If the collection does not implement this interface then
* -1 is returned.
* <p>
* The collection does not have to implement this interface directly.
* If the collection has been decorated using the decorators subpackage
* then these will be removed to access the BoundedCollection.
*
* @param coll the collection to check
* @return the maximum size of the BoundedCollection, -1 if no maximum size
* @throws NullPointerException if the collection is null
*/
public static int maxSize(Collection coll) {
if (coll == null) {
throw new NullPointerException("The collection must not be null");
}
if (coll instanceof BoundedCollection) {
return ((BoundedCollection) coll).maxSize();
}
try {
BoundedCollection bcoll = UnmodifiableBoundedCollection.decorateUsing(coll);
return bcoll.maxSize();
} catch (IllegalArgumentException ex) {
return -1;
}
}
//-----------------------------------------------------------------------
/**
* Returns a collection containing all the elements in <code>collection</code>
* that are also in <code>retain</code>. The cardinality of an element <code>e</code>
* in the returned collection is the same as the cardinality of <code>e</code>
* in <code>collection</code> unless <code>retain</code> does not contain <code>e</code>, in which
* case the cardinality is zero. This method is useful if you do not wish to modify
* the collection <code>c</code> and thus cannot call <code>c.retainAll(retain);</code>.
*
* @param collection the collection whose contents are the target of the #retailAll operation
* @param retain the collection containing the elements to be retained in the returned collection
* @return a <code>Collection</code> containing all the elements of <code>collection</code>
* that occur at least once in <code>retain</code>.
* @throws NullPointerException if either parameter is null
* @since Commons Collections 3.2
*/
public static Collection retainAll(Collection collection, Collection retain) {
return ListUtils.retainAll(collection, retain);
}
/**
* Removes the elements in <code>remove</code> from <code>collection</code>. That is, this
* method returns a collection containing all the elements in <code>c</code>
* that are not in <code>remove</code>. The cardinality of an element <code>e</code>
* in the returned collection is the same as the cardinality of <code>e</code>
* in <code>collection</code> unless <code>remove</code> contains <code>e</code>, in which
* case the cardinality is zero. This method is useful if you do not wish to modify
* the collection <code>c</code> and thus cannot call <code>collection.removeAll(remove);</code>.
*
* @param collection the collection from which items are removed (in the returned collection)
* @param remove the items to be removed from the returned <code>collection</code>
* @return a <code>Collection</code> containing all the elements of <code>collection</code> except
* any elements that also occur in <code>remove</code>.
* @throws NullPointerException if either parameter is null
* @since Commons Collections 3.2
*/
public static Collection removeAll(Collection collection, Collection remove) {
return ListUtils.retainAll(collection, remove);
}
//-----------------------------------------------------------------------
/**
* Returns a synchronized collection backed by the given collection.
* <p>
* You must manually synchronize on the returned buffer's iterator to
* avoid non-deterministic behavior:
*
* <pre>
* Collection c = CollectionUtils.synchronizedCollection(myCollection);
* synchronized (c) {
* Iterator i = c.iterator();
* while (i.hasNext()) {
* process (i.next());
* }
* }
* </pre>
*
* This method uses the implementation in the decorators subpackage.
*
* @param collection the collection to synchronize, must not be null
* @return a synchronized collection backed by the given collection
* @throws IllegalArgumentException if the collection is null
*/
public static Collection synchronizedCollection(Collection collection) {
return SynchronizedCollection.decorate(collection);
}
/**
* Returns an unmodifiable collection backed by the given collection.
* <p>
* This method uses the implementation in the decorators subpackage.
*
* @param collection the collection to make unmodifiable, must not be null
* @return an unmodifiable collection backed by the given collection
* @throws IllegalArgumentException if the collection is null
*/
public static Collection unmodifiableCollection(Collection collection) {
return UnmodifiableCollection.decorate(collection);
}
/**
* Returns a predicated (validating) collection backed by the given collection.
* <p>
* Only objects that pass the test in the given predicate can be added to the collection.
* Trying to add an invalid object results in an IllegalArgumentException.
* It is important not to use the original collection after invoking this method,
* as it is a backdoor for adding invalid objects.
*
* @param collection the collection to predicate, must not be null
* @param predicate the predicate for the collection, must not be null
* @return a predicated collection backed by the given collection
* @throws IllegalArgumentException if the Collection is null
*/
public static Collection predicatedCollection(Collection collection, Predicate predicate) {
return PredicatedCollection.decorate(collection, predicate);
}
/**
* Returns a typed collection backed by the given collection.
* <p>
* Only objects of the specified type can be added to the collection.
*
* @param collection the collection to limit to a specific type, must not be null
* @param type the type of objects which may be added to the collection
* @return a typed collection backed by the specified collection
*/
public static Collection typedCollection(Collection collection, Class type) {
return TypedCollection.decorate(collection, type);
}
/**
* Returns a transformed bag backed by the given collection.
* <p>
* Each object is passed through the transformer as it is added to the
* Collection. It is important not to use the original collection after invoking this
* method, as it is a backdoor for adding untransformed objects.
*
* @param collection the collection to predicate, must not be null
* @param transformer the transformer for the collection, must not be null
* @return a transformed collection backed by the given collection
* @throws IllegalArgumentException if the Collection or Transformer is null
*/
public static Collection transformedCollection(Collection collection, Transformer transformer) {
return TransformedCollection.decorate(collection, transformer);
}
}