1 /*
2 * Copyright (c) 1997, 2012, 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
26 package com.sun.xml.internal.xsom.impl.scd;
27
28 import java.util.Iterator;
29 import java.util.NoSuchElementException;
30 import java.util.Set;
31 import java.util.HashSet;
32 import java.util.Collections;
33
34 /**
35 * Various convenient {@link Iterator} implementations.
36 * @author Kohsuke Kawaguchi
37 */
38 public class Iterators {
39
40 static abstract class ReadOnly<T> implements Iterator<T> {
41 public final void remove() {
42 throw new UnsupportedOperationException();
43 }
44 }
45
46 // we need to run on JDK 1.4
47 private static final Iterator EMPTY = Collections.EMPTY_LIST.iterator();
48
49 public static <T> Iterator<T> empty() {
50 return EMPTY;
51 }
52
53 public static <T> Iterator<T> singleton(T value) {
54 return new Singleton<T>(value);
55 }
56
57 /**
58 * {@link Iterator} that returns a single (or no) value.
59 */
60 static final class Singleton<T> extends ReadOnly<T> {
61 private T next;
62
63 Singleton(T next) {
64 this.next = next;
65 }
66
67 public boolean hasNext() {
68 return next!=null;
69 }
70
71 public T next() {
72 T r = next;
73 next = null;
74 return r;
75 }
76 }
77
78 /**
79 * {@link Iterator} that wraps another {@link Iterator} and changes its type.
80 */
81 public static abstract class Adapter<T,U> extends ReadOnly<T> {
82 private final Iterator<? extends U> core;
83
84 public Adapter(Iterator<? extends U> core) {
85 this.core = core;
86 }
87
88 public boolean hasNext() {
89 return core.hasNext();
90 }
91
92 public T next() {
93 return filter(core.next());
94 }
95
96 protected abstract T filter(U u);
97 }
98
99 /**
100 * For each U, apply U->Iterator<T> function and then iterate all
101 * the resulting T.
102 */
103 public static abstract class Map<T,U> extends ReadOnly<T> {
104 private final Iterator<? extends U> core;
105
106 private Iterator<? extends T> current;
107
108 protected Map(Iterator<? extends U> core) {
109 this.core = core;
110 }
111
112 public boolean hasNext() {
113 while(current==null || !current.hasNext()) {
114 if(!core.hasNext())
115 return false; // nothing more to enumerate
116 current = apply(core.next());
117 }
118 return true;
119 }
120
121 public T next() {
122 return current.next();
123 }
124
125 protected abstract Iterator<? extends T> apply(U u);
126 }
127
128 /**
129 * Filter out objects from another iterator.
130 */
131 public static abstract class Filter<T> extends ReadOnly<T> {
132 private final Iterator<? extends T> core;
133 private T next;
134
135 protected Filter(Iterator<? extends T> core) {
136 this.core = core;
137 }
138
139 /**
140 * Return true to retain the value.
141 */
142 protected abstract boolean matches(T value);
143
144 public boolean hasNext() {
145 while(core.hasNext() && next==null) {
146 next = core.next();
147 if(!matches(next))
148 next = null;
149 }
150
151 return next!=null;
152 }
153
154 public T next() {
155 if(next==null) throw new NoSuchElementException();
156 T r = next;
157 next = null;
158 return r;
159 }
160 }
161
162 /**
163 * Only return unique items.
164 */
165 static final class Unique<T> extends Filter<T> {
166 private Set<T> values = new HashSet<T>();
167 public Unique(Iterator<? extends T> core) {
168 super(core);
169 }
170
171 protected boolean matches(T value) {
172 return values.add(value);
173 }
174 }
175
176 /**
177 * Union of two iterators.
178 */
179 public static final class Union<T> extends ReadOnly<T> {
180 private final Iterator<? extends T> first,second;
181
182 public Union(Iterator<? extends T> first, Iterator<? extends T> second) {
183 this.first = first;
184 this.second = second;
185 }
186
187 public boolean hasNext() {
188 return first.hasNext() || second.hasNext();
189 }
190
191 public T next() {
192 if(first.hasNext()) return first.next();
193 else return second.next();
194 }
195 }
196
197 /**
198 * Array iterator.
199 */
200 public static final class Array<T> extends ReadOnly<T> {
201 private final T[] items;
202 private int index=0;
203 public Array(T[] items) {
204 this.items = items;
205 }
206
207 public boolean hasNext() {
208 return index<items.length;
209 }
210
211 public T next() {
212 return items[index++];
213 }
214 }
215 }