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    1   /*
    2    * Licensed to the Apache Software Foundation (ASF) under one or more
    3    * contributor license agreements.  See the NOTICE file distributed with
    4    * this work for additional information regarding copyright ownership.
    5    * The ASF licenses this file to You under the Apache License, Version 2.0
    6    * (the "License"); you may not use this file except in compliance with
    7    * the License.  You may obtain a copy of the License at
    8    *
    9    *      http://www.apache.org/licenses/LICENSE-2.0
    10   *
    11   * Unless required by applicable law or agreed to in writing, software
    12   * distributed under the License is distributed on an "AS IS" BASIS,
    13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    14   * See the License for the specific language governing permissions and
    15   * limitations under the License.
    16   */
    17  package org.apache.commons.geometry.core.internal;
    18
    19  import java.util.Collection;
    20  import java.util.Deque;
    21  import java.util.Iterator;
    22  import java.util.LinkedList;
    23  import java.util.NoSuchElementException;
    24
    25  /** Class that wraps another iterator, converting each input iterator value into
    26   * one or more output iterator values.
    27   * @param <I> Input iterator type
    28   * @param <T> Output iterator type
    29   */
    30  public abstract class IteratorTransform<I, T> implements Iterator<T> {
    31
    32      /** Input iterator instance that supplies the input values for this instance. */
    33      private final Iterator<I> inputIterator;
    34
    35      /** Output value queue. */
    36      private final Deque<T> outputQueue = new LinkedList<>();
    37
    38      /** Create a new instance that uses the given iterator as the input source.
    39       * @param inputIterator iterator supplying input values
    40       */
    41      protected IteratorTransform(final Iterator<I> inputIterator) {
    42          this.inputIterator = inputIterator;
    43      }
    44
    45      /** {@inheritDoc} */
    46      @Override
    47      public boolean hasNext() {
    48          return loadNextOutput();
    49      }
    50
    51      /** {@inheritDoc} */
    52      @Override
    53      public T next() {
    54          if (outputQueue.isEmpty()) {
    55              throw new NoSuchElementException();
    56          }
    57
    58          return outputQueue.removeFirst();
    59      }
    60
    61      /** Load the next output values into the output queue. Returns true if the output queue
    62       * contains more entries.
    63       * @return true if more output values are available
    64       */
    65      private boolean loadNextOutput() {
    66          while (outputQueue.isEmpty() && inputIterator.hasNext()) {
    67              acceptInput(inputIterator.next());
    68          }
    69
    70          return !outputQueue.isEmpty();
    71      }
    72
    73      /** Add a value to the output queue.
    74       * @param value value to add to the output queue
    75       */
    76      protected void addOutput(final T value) {
    77          outputQueue.add(value);
    78      }
    79
    80      /** Add multiple values to the output queue.
    81       * @param values values to add to the output queue
    82       */
    83      protected void addAllOutput(final Collection<T> values) {
    84          outputQueue.addAll(values);
    85      }
    86
    87      /** Accept a value from the input iterator. This method should take
    88       * the input value and add one or more values to the output queue.
    89       * @param input value from the input iterator
    90       */
    91      protected abstract void acceptInput(I input);
    92  }