org.conqat.lib.commons.collections.UnmodifiableCollection Maven / Gradle / Ivy

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Provides common utility functions
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/*
 * Copyright (c) CQSE GmbH
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.conqat.lib.commons.collections;

import java.io.Serializable;
import java.util.Collection;
import java.util.Collections;

import com.fasterxml.jackson.annotation.JsonIgnore;

/**
 * This is a wrapper for a {@link Collection} prohibiting all calls which would modify its contents.
 * As the construction of this class is performed in constant time it is preferred over copying the
 * collection (which takes linear time). Using this class is also preferred to using the
 * unmodifiableX() in class {@link Collections} as they return the collection base type
 * that does not signal, that the object is unmodifiable. Using the classes in this package makes
 * unmodifiability more explicit.
 * 
 * All prohibited methods throw an {@link UnsupportedOperationException}. The class is nearly the
 * same as the one returned by {@link Collections#unmodifiableCollection(Collection)}, but by making
 * it a public class we can make the return value of some methods more explicit.
 * 
 * This collection is serializable if the wrapped collection is serializable.
 */
public class UnmodifiableCollection implements Collection, Serializable {

	/** Version used for serialization. */
	private static final long serialVersionUID = 1;

	/** The underlying collection. */
	@JsonIgnore
	private final Collection c;

	/**
	 * Creates a new unmodifiable collection from another collection. All modifications to the
	 * underlying collection will directly be visible in this wrapper.
	 */
	public UnmodifiableCollection(Collection c) {
		if (c == null) {
			throw new IllegalArgumentException("Underlying collection may not be null!");
		}
		this.c = c;
	}

	/** {@inheritDoc} */
	@Override
	public boolean isEmpty() {
		return c.isEmpty();
	}

	/** {@inheritDoc} */
	@Override
	public int size() {
		return c.size();
	}

	/** {@inheritDoc} */
	@Override
	public boolean contains(Object o) {
		return c.contains(o);
	}

	/** {@inheritDoc} */
	@Override
	public boolean containsAll(Collection other) {
		return c.containsAll(other);
	}

	/** {@inheritDoc} */
	@Override
	public UnmodifiableIterator iterator() {
		return new UnmodifiableIterator<>(c.iterator());
	}

	/** {@inheritDoc} */
	@Override
	public Object[] toArray() {
		return c.toArray();
	}

	/** {@inheritDoc} */
	@Override
	public  T[] toArray(T[] a) {
		return c.toArray(a);
	}

	/** Operation is not supported. */
	@Override
	public boolean add(E arg0) {
		throw new UnsupportedOperationException();
	}

	/** Operation is not supported. */
	@Override
	public boolean addAll(Collection arg0) {
		throw new UnsupportedOperationException();
	}

	/** Operation is not supported. */
	@Override
	public void clear() {
		throw new UnsupportedOperationException();
	}

	/** Operation is not supported. */
	@Override
	public boolean remove(Object arg0) {
		throw new UnsupportedOperationException();
	}

	/** Operation is not supported. */
	@Override
	public boolean removeAll(Collection arg0) {
		throw new UnsupportedOperationException();
	}

	/** Operation is not supported. */
	@Override
	public boolean retainAll(Collection arg0) {
		throw new UnsupportedOperationException();
	}

	/**
	 * Returns a string representation of this collection.
	 */
	@Override
	public String toString() {
		return c.toString();
	}

	/** {@inheritDoc} */
	@Override
	public boolean equals(Object obj) {
		if (this == obj) {
			return true;
		}
		if (obj instanceof UnmodifiableCollection) {
			return c.equals(((UnmodifiableCollection) obj).c);
		}
		return c.equals(obj);
	}

	/** {@inheritDoc} */
	@Override
	public int hashCode() {
		return c.hashCode();
	}
}