/*

  * 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.utils;

 import java.io.IOException;

 import java.util.Iterator;

 import org.apache.hadoop.io.Writable;

 /**

  * This iterator is designed to deserialize a byte array on the fly to

  * provide new copies of writable objects when desired.  It does not reuse

  * objects, and instead creates a new one for every next().

  *

  * @param <T> Type that extends Writable that will be iterated

  */

 public abstract class ByteStructIterator<T extends Writable> implements

     Iterator<T> {

   /** Data input */

   protected final ExtendedDataInput extendedDataInput;

   /**

    * Wrap ExtendedDataInput in ByteArrayIterator

    *

    * @param extendedDataInput ExtendedDataInput

    */

   public ByteStructIterator(ExtendedDataInput extendedDataInput) {

     this.extendedDataInput = extendedDataInput;

   }

   @Override

   public boolean hasNext() {

     return !extendedDataInput.endOfInput();

   }

   @Override

   public T next() {

     T writable = createWritable();

     try {

       writable.readFields(extendedDataInput);

     } catch (IOException e) {

       throw new IllegalStateException("next: readFields got IOException", e);

     }

     return writable;

   }

   @Override

   public void remove() {

     throw new UnsupportedOperationException("remove: Not supported");

   }

   /**

    * Must be able to create the writable object

    *

    * @return New writable

    */

   protected abstract T createWritable();

 }