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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  }