com.github.mjeanroy.spring.mappers.iterables.LazyUnmodifiableCollectionMapper Maven / Gradle / Ivy

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/**
 * The MIT License (MIT)
 *
 * Copyright (c) 2014 
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

package com.github.mjeanroy.spring.mappers.iterables;

import com.github.mjeanroy.spring.mappers.objects.ObjectMapper;

import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Iterator;

import static com.github.mjeanroy.spring.mappers.commons.PreConditions.notNull;

/**
 * Iterable implementation that map elements from original iterables structure
 * to new iterable element during iteration.
 *
 * This iterable can be considered as a lazy iterable implement since it
 * does not map all elements at instantiation but on only during iteration.
 *
 * Note that this iterable implementation is also a collection implementation, but be
 * careful that this implementation is an unmodifiable collection (it will throw
 * an {@link java.lang.UnsupportedOperationException} for method that will try to
 * modify internal structure).
 *
 * This is a good implementation when {@link #size()} or {@link #isEmpty()}
 * method must be call often.
 *
 * @param  Type of iterable elements.
 * @param  Type of original iterable elements.
 */
public class LazyUnmodifiableCollectionMapper extends AbstractCollection implements Collection, Iterable {

	/**
	 * Original iterable structure.
	 * Each elements will be automatically mapped during iteration.
	 */
	private final Collection from;

	/**
	 * Mapper used to map original iterable structure to new elements.
	 */
	private final ObjectMapper mapper;

	/**
	 * Create new lazy iterable.
	 *
	 * @param from Original iterable structure containing elements to map.
	 * @param mapper Mapper that will be used to map original objects to new objects.
	 */
	public LazyUnmodifiableCollectionMapper(Collection from, ObjectMapper mapper) {
		this.from = notNull(from, "Original iterable must not be null");
		this.mapper = notNull(mapper, "Mapper must not be null");
	}

	@Override
	public Iterator iterator() {
		return new LazyIterableIterator(from.iterator(), mapper);
	}

	@Override
	public int size() {
		return from.size();
	}

	@Override
	public boolean isEmpty() {
		return from.isEmpty();
	}

	@Override
	public boolean add(U u) {
		throw new UnsupportedOperationException();
	}

	@Override
	public boolean remove(Object o) {
		throw new UnsupportedOperationException();
	}

	@Override
	public boolean addAll(Collection collection) {
		throw new UnsupportedOperationException();
	}

	@Override
	public boolean removeAll(Collection collection) {
		throw new UnsupportedOperationException();
	}

	@Override
	public boolean retainAll(Collection collection) {
		throw new UnsupportedOperationException();
	}

	@Override
	public void clear() {
		throw new UnsupportedOperationException();
	}
}