/*
* Copyright 2002-2004 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 org.apache.commons.collections.bag.HashBag;
import org.apache.commons.collections.bag.PredicatedBag;
import org.apache.commons.collections.bag.PredicatedSortedBag;
import org.apache.commons.collections.bag.SynchronizedBag;
import org.apache.commons.collections.bag.SynchronizedSortedBag;
import org.apache.commons.collections.bag.TransformedBag;
import org.apache.commons.collections.bag.TransformedSortedBag;
import org.apache.commons.collections.bag.TreeBag;
import org.apache.commons.collections.bag.TypedBag;
import org.apache.commons.collections.bag.TypedSortedBag;
import org.apache.commons.collections.bag.UnmodifiableBag;
import org.apache.commons.collections.bag.UnmodifiableSortedBag;
/**
* Provides utility methods and decorators for
* {@link Bag} and {@link SortedBag} instances.
*
* @since Commons Collections 2.1
* @version $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
*
* @author Paul Jack
* @author Stephen Colebourne
* @author Andrew Freeman
* @author Matthew Hawthorne
*/
public class BagUtils {
/**
* An empty unmodifiable bag.
*/
public static final Bag EMPTY_BAG = UnmodifiableBag.decorate(new HashBag());
/**
* An empty unmodifiable sorted bag.
*/
public static final Bag EMPTY_SORTED_BAG = UnmodifiableSortedBag.decorate(new TreeBag());
/**
* Instantiation of BagUtils is not intended or required.
* However, some tools require an instance to operate.
*/
public BagUtils() {
}
//-----------------------------------------------------------------------
/**
* Returns a synchronized (thread-safe) bag backed by the given bag.
* In order to guarantee serial access, it is critical that all
* access to the backing bag is accomplished through the returned bag.
* <p>
* It is imperative that the user manually synchronize on the returned
* bag when iterating over it:
*
* <pre>
* Bag bag = BagUtils.synchronizedBag(new HashBag());
* ...
* synchronized(bag) {
* Iterator i = bag.iterator(); // Must be in synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* }
* </pre>
*
* Failure to follow this advice may result in non-deterministic
* behavior.
*
* @param bag the bag to synchronize, must not be null
* @return a synchronized bag backed by that bag
* @throws IllegalArgumentException if the Bag is null
*/
public static Bag synchronizedBag(Bag bag) {
return SynchronizedBag.decorate(bag);
}
/**
* Returns an unmodifiable view of the given bag. Any modification
* attempts to the returned bag will raise an
* {@link UnsupportedOperationException}.
*
* @param bag the bag whose unmodifiable view is to be returned, must not be null
* @return an unmodifiable view of that bag
* @throws IllegalArgumentException if the Bag is null
*/
public static Bag unmodifiableBag(Bag bag) {
return UnmodifiableBag.decorate(bag);
}
/**
* Returns a predicated (validating) bag backed by the given bag.
* <p>
* Only objects that pass the test in the given predicate can be added to the bag.
* Trying to add an invalid object results in an IllegalArgumentException.
* It is important not to use the original bag after invoking this method,
* as it is a backdoor for adding invalid objects.
*
* @param bag the bag to predicate, must not be null
* @param predicate the predicate for the bag, must not be null
* @return a predicated bag backed by the given bag
* @throws IllegalArgumentException if the Bag or Predicate is null
*/
public static Bag predicatedBag(Bag bag, Predicate predicate) {
return PredicatedBag.decorate(bag, predicate);
}
/**
* Returns a typed bag backed by the given bag.
* <p>
* Only objects of the specified type can be added to the bag.
*
* @param bag the bag to limit to a specific type, must not be null
* @param type the type of objects which may be added to the bag
* @return a typed bag backed by the specified bag
*/
public static Bag typedBag(Bag bag, Class type) {
return TypedBag.decorate(bag, type);
}
/**
* Returns a transformed bag backed by the given bag.
* <p>
* Each object is passed through the transformer as it is added to the
* Bag. It is important not to use the original bag after invoking this
* method, as it is a backdoor for adding untransformed objects.
*
* @param bag the bag to predicate, must not be null
* @param transformer the transformer for the bag, must not be null
* @return a transformed bag backed by the given bag
* @throws IllegalArgumentException if the Bag or Transformer is null
*/
public static Bag transformedBag(Bag bag, Transformer transformer) {
return TransformedBag.decorate(bag, transformer);
}
//-----------------------------------------------------------------------
/**
* Returns a synchronized (thread-safe) sorted bag backed by the given
* sorted bag.
* In order to guarantee serial access, it is critical that all
* access to the backing bag is accomplished through the returned bag.
* <p>
* It is imperative that the user manually synchronize on the returned
* bag when iterating over it:
*
* <pre>
* SortedBag bag = BagUtils.synchronizedSortedBag(new TreeBag());
* ...
* synchronized(bag) {
* Iterator i = bag.iterator(); // Must be in synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* }
* </pre>
*
* Failure to follow this advice may result in non-deterministic
* behavior.
*
* @param bag the bag to synchronize, must not be null
* @return a synchronized bag backed by that bag
* @throws IllegalArgumentException if the SortedBag is null
*/
public static SortedBag synchronizedSortedBag(SortedBag bag) {
return SynchronizedSortedBag.decorate(bag);
}
/**
* Returns an unmodifiable view of the given sorted bag. Any modification
* attempts to the returned bag will raise an
* {@link UnsupportedOperationException}.
*
* @param bag the bag whose unmodifiable view is to be returned, must not be null
* @return an unmodifiable view of that bag
* @throws IllegalArgumentException if the SortedBag is null
*/
public static SortedBag unmodifiableSortedBag(SortedBag bag) {
return UnmodifiableSortedBag.decorate(bag);
}
/**
* Returns a predicated (validating) sorted bag backed by the given sorted bag.
* <p>
* Only objects that pass the test in the given predicate can be added to the bag.
* Trying to add an invalid object results in an IllegalArgumentException.
* It is important not to use the original bag after invoking this method,
* as it is a backdoor for adding invalid objects.
*
* @param bag the sorted bag to predicate, must not be null
* @param predicate the predicate for the bag, must not be null
* @return a predicated bag backed by the given bag
* @throws IllegalArgumentException if the SortedBag or Predicate is null
*/
public static SortedBag predicatedSortedBag(SortedBag bag, Predicate predicate) {
return PredicatedSortedBag.decorate(bag, predicate);
}
/**
* Returns a typed sorted bag backed by the given bag.
* <p>
* Only objects of the specified type can be added to the bag.
*
* @param bag the bag to limit to a specific type, must not be null
* @param type the type of objects which may be added to the bag
* @return a typed bag backed by the specified bag
*/
public static SortedBag typedSortedBag(SortedBag bag, Class type) {
return TypedSortedBag.decorate(bag, type);
}
/**
* Returns a transformed sorted bag backed by the given bag.
* <p>
* Each object is passed through the transformer as it is added to the
* Bag. It is important not to use the original bag after invoking this
* method, as it is a backdoor for adding untransformed objects.
*
* @param bag the bag to predicate, must not be null
* @param transformer the transformer for the bag, must not be null
* @return a transformed bag backed by the given bag
* @throws IllegalArgumentException if the Bag or Transformer is null
*/
public static SortedBag transformedSortedBag(SortedBag bag, Transformer transformer) {
return TransformedSortedBag.decorate(bag, transformer);
}
}