heron/common/src/java/com/twitter/heron/common/basics/Pair.java

// Copyright 2016 Twitter. All rights reserved.
//
// 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 com.twitter.heron.common.basics;

import java.util.Objects;

/**
 * Container to ease passing around a tuple of two objects. This object provides a sensible
 * implementation of equals(), returning true if equals() is true on each of the contained
 * objects.
 */
public class Pair<F, S> {
  public final F first;
  public final S second;

  /**
   * Constructor for a Pair.
   *
   * @param first the first object in the Pair
   * @param second the second object in the pair
   */
  public Pair(F first, S second) {
    this.first = first;
    this.second = second;
  }

  /**
   * Convenience method for creating an appropriately typed pair.
   *
   * @param a the first object in the Pair
   * @param b the second object in the pair
   * @return a Pair that is templatized with the types of a and b
   */
  public static <A, B> Pair<A, B> create(A a, B b) {
    return new Pair<A, B>(a, b);
  }

  /**
   * Checks the two objects for equality by delegating to their respective
   * {@link Object#equals(Object)} methods.
   *
   * @param o the {@link Pair} to which this one is to be checked for equality
   * @return true if the underlying objects of the Pair are both considered
   * equal
   */
  @Override
  public boolean equals(Object o) {
    if (!(o instanceof Pair)) {
      return false;
    }
    Pair<?, ?> p = (Pair<?, ?>) o;
    return Objects.equals(p.first, first) && Objects.equals(p.second, second);
  }

  /**
   * Compute a hash code using the hash codes of the underlying objects
   *
   * @return a hashcode of the Pair
   */
  @Override
  public int hashCode() {
    return (first == null ? 0 : first.hashCode()) ^ (second == null ? 0 : second.hashCode());
  }

  /**
   * Returns a string representation of this pair.
   *
   * @return format in "&lt;first, second&gt;"
   */
  @Override
  public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append("<");
    sb.append(this.first == null ? "null" : this.first.toString());
    sb.append(", ");
    sb.append(this.second == null ? "null" : this.second.toString());
    sb.append(">");

    return sb.toString();
  }
}