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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
// http://www.burton-computer.com
//
// Copyright (c) 2013, Burton Computer Corporation
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
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//     Redistributions of source code must retain the above copyright
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//
//     Redistributions in binary form must reproduce the above copyright
//     notice, this list of conditions and the following disclaimer in
//     the documentation and/or other materials provided with the
//     distribution.
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//     Neither the name of the Burton Computer Corporation nor the names
//     of its contributors may be used to endorse or promote products
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//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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package org.javimmutable.collections.cursors;

import org.javimmutable.collections.Cursor;

/**
 * A Cursor that combines multiple Cursors into a single virtual Cursor
 * that visits all values from all Cursors in order.
 *
 * @param 
 */
public class MultiCursor
        implements Cursor
{
    private final Node nodes;
    private final Cursor cursor;

    public MultiCursor(Cursor... cursors)
    {
        Node nodes = null;
        for (int i = cursors.length - 1; i >= 0; --i) {
            nodes = new Node(cursors[i], nodes);
        }
        this.nodes = nodes;
        this.cursor = null;
    }

    private MultiCursor(Node nodes,
                        Cursor cursor)
    {
        this.nodes = nodes;
        this.cursor = cursor;
    }

    public static > MultiCursor of(C cursor1,
                                                             C cursor2)
    {
        return new MultiCursor(new Node(cursor1, new Node(cursor2, null)), null);
    }

    public static > MultiCursor of(C cursor1,
                                                             C cursor2,
                                                             C cursor3)
    {
        return new MultiCursor(new Node(cursor1, new Node(cursor2, new Node(cursor3, null))), null);
    }

    public static > MultiCursor of(C... cursors)
    {
        return new MultiCursor(cursors);
    }

    @Override
    public Cursor next()
    {
        if (cursor != null && cursor.hasValue()) {
            Cursor nextCursor = cursor.next();
            if (nextCursor.hasValue()) {
                return new MultiCursor(nodes, nextCursor);
            }
        }

        Node newNodes = nodes;
        while (newNodes != null) {
            Cursor nextCursor = newNodes.cursor.next();
            if (nextCursor.hasValue()) {
                return new MultiCursor(newNodes.next, nextCursor);
            }
            newNodes = newNodes.next;
        }

        return EmptyCursor.of();
    }

    @Override
    public boolean hasValue()
    {
        if (cursor == null) {
            throw new IllegalStateException();
        }
        return cursor.hasValue();
    }

    @Override
    public T getValue()
    {
        if (cursor == null) {
            throw new IllegalStateException();
        }
        return cursor.getValue();
    }

    public static  Builder builder()
    {
        return new Builder();
    }

    /**
     * Builder class to build a MultiCursor from an arbitrary sequence of Cursors.
     * Cursors will be visited in the same order that add() is called.
     *
     * @param 
     */
    public static class Builder
    {
        private final Node nodes;

        private Builder()
        {
            this(null);
        }

        private Builder(Node nodes)
        {
            this.nodes = nodes;
        }

        public Builder add(Cursor cursor)
        {
            return new Builder(new Node(cursor, nodes));
        }

        public MultiCursor build()
        {
            Node inOrderNodes = null;
            for (Node n = nodes; n != null; n = n.next) {
                inOrderNodes = new Node(n.cursor, inOrderNodes);
            }
            return new MultiCursor(inOrderNodes, null);
        }
    }

    private static class Node
    {
        private final Cursor cursor;
        private final Node next;

        private Node(Cursor cursor,
                     Node next)
        {
            this.cursor = cursor;
            this.next = next;
        }
    }
}