com.googlecode.kevinarpe.papaya.container.UnmodifiableForwardingIterator Maven / Gradle / Ivy

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package com.googlecode.kevinarpe.papaya.container;

/*
 * #%L
 * This file is part of Papaya.
 * %%
 * Copyright (C) 2013 - 2014 Kevin Connor ARPE ([email protected])
 * %%
 * Papaya is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * GPL Classpath Exception:
 * This project is subject to the "Classpath" exception as provided in
 * the LICENSE file that accompanied this code.
 * 
 * Papaya is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with Papaya.  If not, see .
 * #L%
 */

import com.google.common.collect.ForwardingIterator;
import com.googlecode.kevinarpe.papaya.annotation.FullyTested;
import com.googlecode.kevinarpe.papaya.argument.ObjectArgs;

import java.util.Iterator;

/**
 * This class is a simple extension of {@link ForwardingIterator}, where method {@link #remove()}
 * is disabled -- always throws {@link UnsupportedOperationException}.
 * 
 * The class constructor is private.  Instead, use static method {@link #of(Iterator)}.
 * 

 * This class is {@code final} to disable modify-by-inheritance.
 * 

 * Why is this class not called {@code ImmutableIterator}?  Read more here:
 * http://stackoverflow.com/questions/8892350/immutable-vs-unmodifiable-collection
 *
 * @author Kevin Connor ARPE ([email protected])
 *
 * @see ForwardingIterator
 * @see UnmodifiableForwardingListIterator
 * @see #of(Iterator)
 * @see FixedSizeForwardingList#iterator()
 * @see UnmodifiableForwardingList#iterator()
 */
@FullyTested
public final class UnmodifiableForwardingIterator
extends ForwardingIterator {

    /**
     * Returns an unmodifiable view of an underlying {@link Iterator}.  If the input is an instance
     * of {@link UnmodifiableForwardingIterator}, this method avoids wrapping the iterator again --
     * the input value is returned untouched.
     *
     * @param iter
     *        iterator to create an unmodifable view
     *
     * @return an unmodifiable view of underlying iterator
     *
     * @throws NullPointerException
     *         if {@code iter} is {@code null}
     */
    public static  UnmodifiableForwardingIterator of(Iterator iter) {
        ObjectArgs.checkNotNull(iter, "iter");

        if (iter instanceof UnmodifiableForwardingIterator) {
            return (UnmodifiableForwardingIterator) iter;
        }
        return new UnmodifiableForwardingIterator(iter);
    }

    private final Iterator iter;

    private UnmodifiableForwardingIterator(Iterator iter) {
        this.iter = ObjectArgs.checkNotNull(iter, "iter");
    }

    /**
     * This method is final to disable modify-by-inheritance.
     * 

     * {@inheritDoc}
     */
    @Override
    protected final Iterator delegate() {
        return iter;
    }

    /**
     * This method always throws {@link UnsupportedOperationException}.  Also, it is final to
     * disable modify-by-inheritance.
     * 
     * {@inheritDoc}
     */
    @Override
    public final void remove() {
        throw new UnsupportedOperationException(String.format(
            "Class is unmodifiable: %s", this.getClass().getName()));
    }
}