content: /*
   * Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  package openjdk.tools.javac.util;
  
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  import java.util.function.Function;
  import java.util.function.Predicate;
  
  /** Utilities for Iterators.
   *
   *  <p><b>This is NOT part of any supported API.
   *  If you write code that depends on this, you do so at your own risk.
   *  This code and its internal interfaces are subject to change or
   *  deletion without notice.</b>
   */
  public class Iterators {
  
      public static <I, O> Iterator<O> createCompoundIterator(Iterable<I> inputs, Function<I, Iterator<O>> convertor) {
          return new CompoundIterator<>(inputs, convertor);
      }
  
      private static class CompoundIterator<I, O> implements Iterator<O> {
  
          private final Iterator<I> inputs;
          private final Function<I, Iterator<O>> convertor;
          @SuppressWarnings("unchecked")
          private Iterator<O> currentIterator = EMPTY;
  
          public CompoundIterator(Iterable<I> inputs, Function<I, Iterator<O>> convertor) {
              this.inputs = inputs.iterator();
              this.convertor = convertor;
          }
  
          public boolean hasNext() {
              if (currentIterator != null && !currentIterator.hasNext()) {
                  update();
              }
              return currentIterator != null;
          }
  
          public O next() {
              if (currentIterator == EMPTY && !hasNext()) {
                  throw new NoSuchElementException();
              }
              return currentIterator.next();
          }
  
          public void remove() {
              throw new UnsupportedOperationException();
          }
  
          private void update() {
              while (inputs.hasNext()) {
                  currentIterator = convertor.apply(inputs.next());
                  if (currentIterator.hasNext()) return;
              }
              currentIterator = null;
          }
      }
  
      @SuppressWarnings("rawtypes")
      private static final Iterator EMPTY = new Iterator() {
          public boolean hasNext() {
              return false;
          }
  
          @Override
          public Object next() {
              return null;
          }
      };
  
      public static <E> Iterator<E> createFilterIterator(Iterator<E> input, Predicate<E> test) {
          return new Iterator<E>() {
              private E current = update();
              private E update () {
                  while (input.hasNext()) {
                      E sym = input.next();
                      if (test.test(sym)) {
                          return sym;
                      }
                  }
  
                  return null;
              }
              @Override
              public boolean hasNext() {
                  return current != null;
              }
  
              @Override
              public E next() {
                  E res = current;
                  current = update();
                  return res;
              }
          };
      }
  
  }
  