Iterators.java revision 3735:85a8bfb00296
1/* 2 * Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26package com.sun.tools.javac.util; 27 28import java.util.Iterator; 29import java.util.NoSuchElementException; 30import java.util.function.Function; 31 32/** Utilities for Iterators. 33 * 34 * <p><b>This is NOT part of any supported API. 35 * If you write code that depends on this, you do so at your own risk. 36 * This code and its internal interfaces are subject to change or 37 * deletion without notice.</b> 38 */ 39public class Iterators { 40 41 public static <I, O> Iterator<O> createCompoundIterator(Iterable<I> inputs, Function<I, Iterator<O>> convertor) { 42 return new CompoundIterator<>(inputs, convertor); 43 } 44 45 private static class CompoundIterator<I, O> implements Iterator<O> { 46 47 private final Iterator<I> inputs; 48 private final Function<I, Iterator<O>> convertor; 49 @SuppressWarnings("unchecked") 50 private Iterator<O> currentIterator = EMPTY; 51 52 public CompoundIterator(Iterable<I> inputs, Function<I, Iterator<O>> convertor) { 53 this.inputs = inputs.iterator(); 54 this.convertor = convertor; 55 } 56 57 public boolean hasNext() { 58 if (currentIterator != null && !currentIterator.hasNext()) { 59 update(); 60 } 61 return currentIterator != null; 62 } 63 64 public O next() { 65 if (currentIterator == EMPTY && !hasNext()) { 66 throw new NoSuchElementException(); 67 } 68 return currentIterator.next(); 69 } 70 71 public void remove() { 72 throw new UnsupportedOperationException(); 73 } 74 75 private void update() { 76 while (inputs.hasNext()) { 77 currentIterator = convertor.apply(inputs.next()); 78 if (currentIterator.hasNext()) return; 79 } 80 currentIterator = null; 81 } 82 } 83 84 @SuppressWarnings("rawtypes") 85 private final static Iterator EMPTY = new Iterator() { 86 public boolean hasNext() { 87 return false; 88 } 89 90 @Override 91 public Object next() { 92 return null; 93 } 94 }; 95} 96