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Library providing immutable/persistent collection classes for Java. While collections are immutable they provide methods for adding and removing values by creating new modified copies of themselves. Each copy shares almost all of its structure with other copies to minimize memory consumption.

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// Burton Computer Corporation
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package org.javimmutable.collections.cursors;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Holder;
import org.javimmutable.collections.Holders;

import javax.annotation.concurrent.Immutable;
import java.util.Iterator;

/**
 * Provides objects implementing the Cursor interface that can be used to traverse
 * an Iterable.  The Cursors are not actually immutable but are designed to behave
 * as though they are.  However since they depend on a mutable object tied to a
 * mutable collection for their state they are not thread safe.  They should only
 * be used when no other threads could be modifying the underlying collection.
 * Also their next() methods can throw exceptions due to concurrent modification
 * of the collection.
 */
@Immutable
public abstract class IterableCursor
{
    /**
     * Creates a mutable Cursor implementation that traverses the specified iterable.  Note that because
     * the Iterator and the collection it points to are not immutable outside factors can interfere with
     * the operation of this class.  In particular this class is not thread safe so the caller must take
     * precautions to synchronize access to the underlying collection.
     * 
     * The Cursor retains information obtained from the Iterator so that multiple passes can be made over
     * the data, intermediate Cursor values can be saved and resumed for look-ahead etc.
     */
    public static  Cursor of(Iterable iterable)
    {
        return ValueFunctionCursor.of(new Factory(iterable));
    }

    private static class Factory
        implements ValueFunctionFactory>
    {
        private final Iterable iterable;

        private Factory(Iterable iterable)
        {
            this.iterable = iterable;
        }

        @Override
        public Function createFunction()
        {
            return new Function(iterable.iterator());
        }
    }

    private static class Function
        implements ValueFunction
    {
        private final Iterator iterator;

        private Function(Iterator iterator)
        {
            this.iterator = iterator;
        }

        @Override
        public Holder nextValue()
        {
            return iterator.hasNext() ? Holders.of(iterator.next()) : Holders.of();
        }
    }
}