ImmutablePair.java

/*
 * Copyright © 2014 Cask Data, Inc.
 *
 * 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 co.cask.cdap.common.utils;

import com.google.common.base.Objects;

/**
 * An {@link ImmutablePair} consists of two elements within. The elements once set
 * in the ImmutablePair cannot be modified. The class itself is final, so that it
 * cannot be subclassed. This is general norm for creating Immutable classes.
 * Please note that the {@link ImmutablePair} cannot be modified once set, but the
 * objects within them can be, so in general it means that if there are mutable objects
 * within the pair then the pair itself is effectively mutable.
 *
 * <pre>
 *   ImmutablePair<Tuple, TupleInputStreamIdentifier> tupleStreamPair= new
 *    ImmutablePair<Tuple, TupleInputStreamIdentifier> (tuple, identifier);
 *   ...
 *   ...
 *   Tuple t = tupleStreamPair.getFirst();
 *   TupleInputStreamIdentifier identifier = tupleStreamPair.getSecond();
 *   ...
 * </pre>
 *
 * @param <A> type A
 * @param <B> type B
 */
public final class ImmutablePair<A, B> {
  private final A first;
  private final B second;

  public static <A, B> ImmutablePair<A, B> of(A first, B second) {
    return new ImmutablePair<>(first, second);
  }

  /**
   * Constructs a Immutable Pair.
   * @param first object in pair
   * @param second object in pair
   */
  public ImmutablePair(A first, B second) {
    this.first = first;
    this.second = second;
  }

  /**
   * Returns first object from pair.
   * @return first object from pair.
   */
  public A getFirst() {
    return first;
  }

  /**
   * Return second object from pair.
   * @return second object from pair.
   */
  public B getSecond() {
    return second;
  }

  /**
   * Returns a string representation of {@link ImmutablePair} object.
   * @return string representation of this object.
   */
  @Override
  public String toString() {
    return Objects.toStringHelper(this)
            .add("first", first)
            .add("second", second)
            .toString();
  }

  /**
   * Returns a hash code value for this object.
   * @return hash code value of this object.
   */
  @Override
  public int hashCode() {
    return Objects.hashCode(first, second);
  }

  /**
   * Returns whether some other object "is equal" to this object.
   * @param o reference object with which to compare
   * @return true if object is the same as the obj argument; false otherwise.
   */
  @Override
  public boolean equals(Object o) {
    if (o == null) {
      return false;
    }
    if (!(o instanceof ImmutablePair)) {
      return false;
    }
    ImmutablePair<?, ?> other = (ImmutablePair<?, ?>) o;
    return Objects.equal(first, other.first) && Objects.equal(second, other.second);
  }
}