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GS Collections is a collections framework for Java. It has JDK-compatible List, Set and Map implementations with a rich API and set of utility classes that work with any JDK compatible Collections, Arrays, Maps or Strings. The iteration protocol was inspired by the Smalltalk collection framework.

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/*
 * Copyright 2013 Goldman Sachs.
 *
 * 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.gs.collections.impl.bag.immutable;

import com.gs.collections.api.bag.Bag;
import com.gs.collections.api.bag.ImmutableBag;
import com.gs.collections.api.factory.bag.ImmutableBagFactory;
import com.gs.collections.impl.utility.Iterate;
import net.jcip.annotations.Immutable;

@Immutable
public final class ImmutableBagFactoryImpl implements ImmutableBagFactory
{
    public  ImmutableBag of()
    {
        return this.with();
    }

    public  ImmutableBag with()
    {
        return (ImmutableBag) ImmutableEmptyBag.INSTANCE;
    }

    public  ImmutableBag of(T element)
    {
        return this.with(element);
    }

    public  ImmutableBag with(T element)
    {
        return new ImmutableSingletonBag(element);
    }

    public  ImmutableBag of(T... elements)
    {
        return this.with(elements);
    }

    public  ImmutableBag with(T... elements)
    {
        if (elements == null || elements.length == 0)
        {
            return this.of();
        }
        if (elements.length == 1)
        {
            return this.of(elements[0]);
        }
        if (elements.length < ImmutableArrayBag.MAXIMUM_USEFUL_ARRAY_BAG_SIZE)
        {
            return ImmutableArrayBag.newBagWith(elements);
        }
        return ImmutableHashBag.newBagWith(elements);
    }

    public  ImmutableBag ofAll(Iterable items)
    {
        return this.withAll(items);
    }

    public  ImmutableBag withAll(Iterable items)
    {
        if (items instanceof ImmutableBag)
        {
            return (ImmutableBag) items;
        }
        if (items instanceof Bag)
        {
            Bag bag = (Bag) items;
            if (bag.isEmpty())
            {
                return this.with();
            }
            if (bag.size() == 1)
            {
                return this.with(bag.getFirst());
            }
            if (bag.sizeDistinct() < ImmutableArrayBag.MAXIMUM_USEFUL_ARRAY_BAG_SIZE)
            {
                return ImmutableArrayBag.copyFrom(bag);
            }
            return new ImmutableHashBag(bag);
        }
        return this.of((T[]) Iterate.toArray(items));
    }
}