/*
    * 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.edge;
  
  import org.apache.hadoop.io.NullWritable;
  import org.apache.hadoop.io.WritableComparable;
  
  /**
   * An edge that has no value.
   *
   * @param <I> Vertex ID
   */
  public class EdgeNoValue<I extends WritableComparable>
      implements ReusableEdge<I, NullWritable> {
    /** Target vertex id */
    private I targetVertexId = null;
  
    /** Empty constructor */
    EdgeNoValue() { }
  
    /**
     * Constructor with target vertex ID. Don't call, use EdgeFactory instead.
     *
     * @param targetVertexId vertex ID
     */
    EdgeNoValue(I targetVertexId) {
      this.targetVertexId = targetVertexId;
    }
  
    @Override
    public void setTargetVertexId(I targetVertexId) {
      this.targetVertexId = targetVertexId;
    }
  
    @Override
    public void setValue(NullWritable value) {
      // do nothing
    }
  
    @Override
    public I getTargetVertexId() {
      return targetVertexId;
    }
  
    @Override
    public NullWritable getValue() {
      return NullWritable.get();
    }
  
    @Override
    public String toString() {
      return "(targetVertexId = " + targetVertexId + ")";
    }
  }