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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) 2021, 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:
//
//     Redistributions of source code must retain the above copyright
//     notice, this list of conditions and the following disclaimer.
//
//     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.
//
//     Neither the name of the Burton Computer Corporation nor the names
//     of its contributors may be used to endorse or promote products
//     derived from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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package org.javimmutable.collections.list;

import org.javimmutable.collections.Func2;
import org.javimmutable.collections.Proc1Throws;
import org.javimmutable.collections.Sum1Throws;
import org.javimmutable.collections.common.ToStringHelper;
import org.javimmutable.collections.iterators.GenericIterator;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.Immutable;
import java.util.function.Consumer;

@Immutable
class EmptyNode
    extends AbstractNode
{
    private static EmptyNode INSTANCE = new EmptyNode();

    private EmptyNode()
    {
    }

    @SuppressWarnings("unchecked")
    static  EmptyNode instance()
    {
        return INSTANCE;
    }

    @Override
    boolean isEmpty()
    {
        return true;
    }

    @Override
    int size()
    {
        return 0;
    }

    @Override
    int depth()
    {
        return 0;
    }

    @Override
    T get(int index)
    {
        throw new IndexOutOfBoundsException();
    }

    @Nonnull
    @Override
    AbstractNode append(T value)
    {
        return new OneValueNode<>(value);
    }

    @Nonnull
    @Override
    AbstractNode append(@Nonnull AbstractNode node)
    {
        return node;
    }

    @Nonnull
    @Override
    AbstractNode prepend(T value)
    {
        return new OneValueNode<>(value);
    }

    @Nonnull
    @Override
    AbstractNode prepend(@Nonnull AbstractNode node)
    {
        return node;
    }

    @Nonnull
    @Override
    AbstractNode assign(int index,
                           T value)
    {
        throw new IndexOutOfBoundsException();
    }

    @Nonnull
    @Override
    AbstractNode insert(int index,
                           T value)
    {
        if (index == 0) {
            return new OneValueNode<>(value);
        } else {
            throw new IndexOutOfBoundsException();
        }
    }

    @Nonnull
    @Override
    AbstractNode delete(int index)
    {
        throw new IndexOutOfBoundsException();
    }

    @Nonnull
    @Override
    AbstractNode deleteFirst()
    {
        throw new IndexOutOfBoundsException();
    }

    @Nonnull
    @Override
    AbstractNode deleteLast()
    {
        throw new IndexOutOfBoundsException();
    }

    @Nonnull
    @Override
    AbstractNode prefix(int limit)
    {
        if (limit == 0) {
            return this;
        } else {
            throw new IndexOutOfBoundsException();
        }
    }

    @Override
    void copyTo(T[] array,
                int offset)
    {
    }

    @Nonnull
    @Override
    AbstractNode suffix(int offset)
    {
        if (offset == 0) {
            return this;
        } else {
            throw new IndexOutOfBoundsException();
        }
    }

    @Nonnull
    @Override
    AbstractNode reverse()
    {
        return this;
    }

    @Nullable
    @Override
    public GenericIterator.State iterateOverRange(@Nullable GenericIterator.State parent,
                                                     int offset,
                                                     int limit)
    {
        assert offset == 0 && limit == 0;
        return parent;
    }

    @Override
    public void forEach(Consumer action)
    {
    }

    @Override
    public  void forEachThrows(@Nonnull Proc1Throws proc)
        throws E
    {
    }

    @Override
    public  V reduce(V initialValue,
                        Func2 accumulator)
    {
        return initialValue;
    }

    @Override
    public  V reduceThrows(V initialValue,
                                                   Sum1Throws accumulator)
        throws E
    {
        return initialValue;
    }

    @Override
    public void checkInvariants()
    {
    }

    @Override
    public String toString()
    {
        final StringBuilder sb = new StringBuilder();
        sb.append("[");
        forEach(value -> ToStringHelper.addToString(sb, 1, value));
        sb.append("]");
        return sb.toString();
    }
}