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 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.commons.lang3.tuple;

import java.io.Serializable;
import java.util.Objects;

import org.apache.commons.lang3.builder.CompareToBuilder;

A triple consisting of three elements.
This class is an abstract implementation defining the basic API.
It refers to the elements as 'left', 'middle' and 'right'.
Subclass implementations may be mutable or immutable.
However, there is no restriction on the type of the stored objects that may be stored.
If mutable objects are stored in the triple, then the triple itself effectively becomes mutable.
Type parameters:
<L> – the left element type
<M> – the middle element type
<R> – the right element type
Since:
3.2/**
 * <p>A triple consisting of three elements.</p>
 *
 * <p>This class is an abstract implementation defining the basic API.
 * It refers to the elements as 'left', 'middle' and 'right'.</p>
 *
 * <p>Subclass implementations may be mutable or immutable.
 * However, there is no restriction on the type of the stored objects that may be stored.
 * If mutable objects are stored in the triple, then the triple itself effectively becomes mutable.</p>
 *
 * @param <L> the left element type
 * @param <M> the middle element type
 * @param <R> the right element type
 *
 * @since 3.2
 */
public abstract class Triple<L, M, R> implements Comparable<Triple<L, M, R>>, Serializable {

    private static final class TripleAdapter<L, M, R> extends Triple<L, M, R> {

        private static final long serialVersionUID = 1L;

        @Override
        public L getLeft() {
            return null;
        }

        @Override
        public M getMiddle() {
            return null;
        }

        @Override
        public R getRight() {
            return null;
        }

    }

    
Serialization version /** Serialization version */
    private static final long serialVersionUID = 1L;

    
An empty array.
 Consider using emptyArray() to avoid generics warnings. 
Since:
3.10./**
     * An empty array.
     * <p>
     * Consider using {@link #emptyArray()} to avoid generics warnings.
     * </p>
     *
     * @since 3.10.
     */
    public static final Triple<?, ?, ?>[] EMPTY_ARRAY = new TripleAdapter[0];

    
Returns the empty array singleton that can be assigned without compiler warning.
Type parameters:
<L> – the left element type
<M> – the middle element type
<R> – the right element type
Returns:
the empty array singleton that can be assigned without compiler warning.
Since:
3.10./**
     * Returns the empty array singleton that can be assigned without compiler warning.
     *
     * @param <L> the left element type
     * @param <M> the middle element type
     * @param <R> the right element type
     * @return the empty array singleton that can be assigned without compiler warning.
     *
     * @since 3.10.
     */
    @SuppressWarnings("unchecked")
    public static <L, M, R> Triple<L, M, R>[] emptyArray() {
        return (Triple<L, M, R>[]) EMPTY_ARRAY;
    }

    
Obtains an immutable triple of three objects inferring the generic types.
This factory allows the triple to be created using inference to
obtain the generic types.
Params:
left –  the left element, may be null
middle – the middle element, may be null
right –  the right element, may be null
Type parameters:
<L> – the left element type
<M> – the middle element type
<R> – the right element type
Returns:
a triple formed from the three parameters, not null/**
     * <p>Obtains an immutable triple of three objects inferring the generic types.</p>
     *
     * <p>This factory allows the triple to be created using inference to
     * obtain the generic types.</p>
     *
     * @param <L> the left element type
     * @param <M> the middle element type
     * @param <R> the right element type
     * @param left  the left element, may be null
     * @param middle the middle element, may be null
     * @param right  the right element, may be null
     * @return a triple formed from the three parameters, not null
     */
    public static <L, M, R> Triple<L, M, R> of(final L left, final M middle, final R right) {
        return new ImmutableTriple<>(left, middle, right);
    }

    //-----------------------------------------------------------------------
    
Compares the triple based on the left element, followed by the middle element, finally the right element. The types must be Comparable.
Params:
other –  the other triple, not null
Returns:
negative if this is less, zero if equal, positive if greater/**
     * <p>Compares the triple based on the left element, followed by the middle element,
     * finally the right element.
     * The types must be {@code Comparable}.</p>
     *
     * @param other  the other triple, not null
     * @return negative if this is less, zero if equal, positive if greater
     */
    @Override
    public int compareTo(final Triple<L, M, R> other) {
      return new CompareToBuilder().append(getLeft(), other.getLeft())
          .append(getMiddle(), other.getMiddle())
          .append(getRight(), other.getRight()).toComparison();
    }

    
Compares this triple to another based on the three elements.
Params:
obj –  the object to compare to, null returns false
Returns:
true if the elements of the triple are equal/**
     * <p>Compares this triple to another based on the three elements.</p>
     *
     * @param obj  the object to compare to, null returns false
     * @return true if the elements of the triple are equal
     */
    @Override
    public boolean equals(final Object obj) {
        if (obj == this) {
            return true;
        }
        if (obj instanceof Triple<?, ?, ?>) {
            final Triple<?, ?, ?> other = (Triple<?, ?, ?>) obj;
            return Objects.equals(getLeft(), other.getLeft())
                && Objects.equals(getMiddle(), other.getMiddle())
                && Objects.equals(getRight(), other.getRight());
        }
        return false;
    }

    //-----------------------------------------------------------------------
    
Gets the left element from this triple.
Returns:
the left element, may be null/**
     * <p>Gets the left element from this triple.</p>
     *
     * @return the left element, may be null
     */
    public abstract L getLeft();

    
Gets the middle element from this triple.
Returns:
the middle element, may be null/**
     * <p>Gets the middle element from this triple.</p>
     *
     * @return the middle element, may be null
     */
    public abstract M getMiddle();

    
Gets the right element from this triple.
Returns:
the right element, may be null/**
     * <p>Gets the right element from this triple.</p>
     *
     * @return the right element, may be null
     */
    public abstract R getRight();

    
Returns a suitable hash code.
Returns:
the hash code/**
     * <p>Returns a suitable hash code.</p>
     *
     * @return the hash code
     */
    @Override
    public int hashCode() {
        return Objects.hashCode(getLeft()) ^ Objects.hashCode(getMiddle()) ^ Objects.hashCode(getRight());
    }

    
Returns a String representation of this triple using the format ($left,$middle,$right).
Returns:
a string describing this object, not null/**
     * <p>Returns a String representation of this triple using the format {@code ($left,$middle,$right)}.</p>
     *
     * @return a string describing this object, not null
     */
    @Override
    public String toString() {
        return "(" + getLeft() + "," + getMiddle() + "," + getRight() + ")";
    }

    
Formats the receiver using the given format.
This uses Formattable to perform the formatting. Three variables may be used to embed the left and right elements. Use %1$s for the left element, %2$s for the middle and %3$s for the right element. The default format used by toString() is (%1$s,%2$s,%3$s).
Params:
format –  the format string, optionally containing %1$s, %2$s and %3$s, not null
Returns:
the formatted string, not null/**
     * <p>Formats the receiver using the given format.</p>
     *
     * <p>This uses {@link java.util.Formattable} to perform the formatting. Three variables may
     * be used to embed the left and right elements. Use {@code %1$s} for the left
     * element, {@code %2$s} for the middle and {@code %3$s} for the right element.
     * The default format used by {@code toString()} is {@code (%1$s,%2$s,%3$s)}.</p>
     *
     * @param format  the format string, optionally containing {@code %1$s}, {@code %2$s} and {@code %3$s}, not null
     * @return the formatted string, not null
     */
    public String toString(final String format) {
        return String.format(format, getLeft(), getMiddle(), getRight());
    }

}