/*

  * 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.giraph.writable.tuple;

 import java.io.DataInput;

 import java.io.DataOutput;

 import java.io.IOException;

 import org.apache.commons.lang3.tuple.Pair;

 import org.apache.hadoop.io.Writable;

 /**

  * Pair Writable class, that knows types upfront and can deserialize itself.

  *

  * PairWritable knows types, as instances are passed through constructor, and

  * are references are immutable (values themselves are mutable).

  *

  * Child classes specify no-arg constructor that passes concrete types in.

  *

  * Extends Pair, not ImmutablePair, since later class is final. Code is

  * copied from it.

  *

  * @param <L> Type of the left element

  * @param <R> Type of the right element

  */

 public class PairWritable<L extends Writable, R extends Writable>

     extends Pair<L, R> implements Writable {

   /** Left object */

   private final L left;

   /** Right object */

   private final R right;

   /**

    * Create a new pair instance.

    *

    * @param left  the left value

    * @param right  the right value

    */

   public PairWritable(L left, R right) {

     this.left = left;

     this.right = right;

   }

   /**

    * <p>

    * Obtains an immutable pair of from two objects inferring

    * the generic types.</p>

    *

    * <p>This factory allows the pair to be created using inference to

    * obtain the generic types.</p>

    *

    * @param <L> the left element type

    * @param <R> the right element type

    * @param left  the left element, may be null

    * @param right  the right element, may be null

    * @return a pair formed from the two parameters, not null

    */

   public static <L extends Writable, R extends Writable>

   PairWritable<L, R> of(L left, R right) {

     return new PairWritable<L, R>(left, right);

   }

   @Override

   public final L getLeft() {

     return left;

   }

   @Override

   public final R getRight() {

     return right;

   }

   /**

    * <p>Throws {@code UnsupportedOperationException}.</p>

    *

    * <p>This pair is immutable, so this operation is not supported.</p>

    *

    * @param value  the value to set

    * @return never

    * @throws UnsupportedOperationException as this operation is not supported

    */

   @Override

   public final R setValue(R value) {

     throw new UnsupportedOperationException();

   }

   @Override

   public final void write(DataOutput out) throws IOException {

     left.write(out);

     right.write(out);

   }

   @Override

   public final void readFields(DataInput in) throws IOException {

     left.readFields(in);

     right.readFields(in);

   }

 }