https://github.com/eclipse/eclipse-collections/eclipse-collections: Eclipse 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.
  • Craig P. Motlin
  • Donald Raab
  • Mohammad A. Rezaei
  • Hiroshi Ito
  • Nikhil J. Nanivadekar 
/*
 * Copyright (c) 2016 Goldman Sachs.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Eclipse Distribution License v. 1.0 which accompany this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 */

package org.eclipse.collections.impl.list.immutable;

import java.io.Serializable;
import java.util.RandomAccess;

import org.eclipse.collections.api.block.procedure.Procedure;
import org.eclipse.collections.api.factory.Lists;
import org.eclipse.collections.api.list.ImmutableList;


This is a three element immutable List which is created by calling
Immutable.newListWith(one, two, three) method.

/**
 * This is a three element immutable List which is created by calling
 * Immutable.newListWith(one, two, three) method.
 */
final class ImmutableTripletonList<T>
        extends AbstractImmutableList<T>
        implements Serializable, RandomAccess
{
    private static final long serialVersionUID = 1L;

    private final T element1;
    private final T element2;
    private final T element3;

    ImmutableTripletonList(T obj1, T obj2, T obj3)
    {
        this.element1 = obj1;
        this.element2 = obj2;
        this.element3 = obj3;
    }

    @Override
    public int size()
    {
        return 3;
    }

    @Override
    public void each(Procedure<? super T> procedure)
    {
        procedure.value(this.element1);
        procedure.value(this.element2);
        procedure.value(this.element3);
    }

    @Override
    public T get(int index)
    {
        switch (index)
        {
            case 0:
                return this.element1;
            case 1:
                return this.element2;
            case 2:
                return this.element3;
            default:
                throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + this.size());
        }
    }

    @Override
    public T getOnly()
    {
        throw new IllegalStateException("Size must be 1 but was " + this.size());
    }

    @Override
    public ImmutableList<T> newWith(T newItem)
    {
        return Lists.immutable.with(this.element1, this.element2, this.element3, newItem);
    }
}