Triple.java

/*
 * Copyright 2016 Christoph Böhme
 *
 * 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.culturegraph.mf.framework.objects;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Objects;

/**
 * Stores an immutable subject-predicate-object triple.
 *
 * @author Markus Michael Geipel
 */
public final class Triple implements Comparable<Triple> {

	private final String subject;
	private final String predicate;
	private final String object;
	private final ObjectType objectType;

	private final int preCompHashCode;

	public Triple(final String subject, final String predicate,
			final String object) {
		this(subject, predicate, object, ObjectType.STRING);
	}

	public Triple(final String subject, final String predicate,
			final String object, final ObjectType objectType) {
		this.subject = subject;
		this.predicate = predicate;
		this.object = object;
		this.objectType = objectType;
		preCompHashCode = computeHashCode();
	}

	private int computeHashCode() {
		return Objects.hash(subject, predicate, object, objectType);
	}

	public String getSubject() {
		return subject;
	}

	public String getPredicate() {
		return predicate;
	}

	public String getObject() {
		return object;
	}

	public ObjectType getObjectType() {
		return objectType;
	}

	public static Triple read(final ObjectInputStream in) throws IOException {
		try {
			return new Triple(in.readUTF(), in.readUTF(), in.readUTF(),
					(ObjectType) in.readObject());
		} catch (final ClassNotFoundException e) {
			throw new IOException("Cannot read triple", e);
		}
	}

	public void write(final ObjectOutputStream out) throws IOException {
		out.writeUTF(subject);
		out.writeUTF(predicate);
		out.writeUTF(object);
		out.writeObject(objectType);
	}

	@Override
	public int hashCode() {
		return preCompHashCode;
	}

	@Override
	public boolean equals(final Object obj) {
		if (obj == this) {
			return true;
		}
		if (!(obj instanceof Triple)) {
			return false;
		}
		final Triple other = (Triple) obj;
		return other.preCompHashCode == preCompHashCode
				&& other.predicate.equals(predicate)
				&& other.object.equals(object)
				&& other.subject.equals(subject)
				&& other.objectType == objectType;
	}

	@Override
	public int compareTo(final Triple triple) {
		int result = subject.compareTo(triple.subject);
		if (result == 0) {
			result = predicate.compareTo(triple.predicate);
			if (result == 0) {
				result = object.compareTo(triple.object);
				if(result == 0) {
					return objectType.compareTo(triple.objectType);
				}
			}
		}
		return result;
	}

	@Override
	public String toString() {
		return subject + ":" + predicate + "=" + object + " (" + objectType + ")";
	}

	/**
	 * Content type of triple object.
	 */
	public enum ObjectType {
		STRING, ENTITY
	}

}