/**
    *
    * 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.hadoop.hbase.util;
  
  import java.util.Iterator;
  
  import org.apache.commons.lang.NotImplementedException;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  
  /**
   * A generic, immutable class for pairs of objects both of type <code>T</code>.
   * @param <T>
   * @see Pair if Types differ.
   */
  @InterfaceAudience.Public
  @InterfaceStability.Stable
  public class PairOfSameType<T> implements Iterable<T> {
    private final T first;
    private final T second;
  
    /**
     * Constructor
     * @param a operand
     * @param b operand
     */
    public PairOfSameType(T a, T b) {
      this.first = a;
      this.second = b;
    }
  
    /**
     * Return the first element stored in the pair.
     * @return T
     */
    public T getFirst() {
      return first;
    }
  
    /**
     * Return the second element stored in the pair.
     * @return T
     */
    public T getSecond() {
      return second;
    }
  
    private static boolean equals(Object x, Object y) {
       return (x == null && y == null) || (x != null && x.equals(y));
    }
  
    @Override
    @SuppressWarnings("unchecked")
    public boolean equals(Object other) {
      return other instanceof PairOfSameType &&
        equals(first, ((PairOfSameType)other).first) &&
        equals(second, ((PairOfSameType)other).second);
    }
  
    @Override
    public int hashCode() {
      if (first == null)
        return (second == null) ? 0 : second.hashCode() + 1;
      else if (second == null)
        return first.hashCode() + 2;
      else
        return first.hashCode() * 17 + second.hashCode();
    }
  
    @Override
    public String toString() {
      return "{" + getFirst() + "," + getSecond() + "}";
    }
  
    @Override
    public Iterator<T> iterator() {
      return new Iterator<T>() {
        private int returned = 0;
  
        @Override
        public boolean hasNext() {
          return this.returned < 2;
       }
 
       @Override
       public T next() {
         if (++this.returned == 1) return getFirst();
         else if (this.returned == 2) return getSecond();
         else throw new IllegalAccessError("this.returned=" + this.returned);
       }
 
       @Override
       public void remove() {
         throw new NotImplementedException();
       }
     };
   }
 }