1 /*
2 * Copyright (c) 2010, 2017, 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 javafx.collections;
27
28 import java.util.Collections;
29 import java.util.List;
30
31 /**
32 * Interface that receives notifications of changes to an ObservableList.
33 *
34 * @param <E> the list element type
35 * @see Change
36 * @since JavaFX 2.0
37 */
38 @FunctionalInterface
39 public interface ListChangeListener<E> {
40
41 /**
42 * Represents a report of changes done to an {@link ObservableList}. The change may consist of one or more actual
43 * changes and must be iterated by calling the {@link #next()} method.
44 *
45 * Each change must be one of the following:
46 * <ul>
47 * <li><b>Permutation change</b> : {@link #wasPermutated()} returns true in this case.
48 * The permutation happened at range between {@link #getFrom() from} (inclusive) and {@link #getTo() to} (exclusive) and
49 * can be queried by calling {@link #getPermutation(int)} method.
50 * <li><b>Add or remove change</b> : In this case, at least one of the {@link #wasAdded()}, {@link #wasRemoved()} returns true.
51 * If both methods return true, {@link #wasReplaced()} will also return true.
52 * <p>The {@link #getRemoved()} method returns a list of elements that have been
53 * replaced or removed from the list.
54 * <p> The range between {@link #getFrom() from} (inclusive) and {@link #getTo() to} (exclusive)
55 * denotes the sublist of the list that contain new elements. Note that this is a half-open
56 * interval, so if no elements were added, {@code getFrom()} is equal to {@code getTo()}.
57 * <p>It is possible to get a list of added elements by calling getAddedSubList().
58 * <p>Note that in order to maintain correct indexes of the separate add/remove changes, these changes
59 * <b>must</b> be sorted by their {@code from} index.
60 * <li><b>Update change</b> : {@link #wasUpdated()} return true on an update change.
61 * All elements between {@link #getFrom() from} (inclusive) and {@link #getTo() to} (exclusive) were updated.
62 * </ul>
63 *
64 * <b>Important:</b> It's necessary to call {@link #next()} method before calling
65 * any other method of {@code Change}. The same applies after calling {@link #reset()}.
66 * The only methods that works at any time is {@link #getList()}.
67 *
68 *<p>
69 * Typical usage is to observe changes on an ObservableList in order
70 * to hook or unhook (or add or remove a listener) or in order to maintain
71 * some invariant on every element in that ObservableList. A common code
72 * pattern for doing this looks something like the following:<br>
73 *
74 * <blockquote><pre>
75 * ObservableList<Item> theList = ...;
76 *
77 * theList.addListener(new ListChangeListener<Item>() {
78 * public void onChanged(Change<Item> c) {
79 * while (c.next()) {
80 * if (c.wasPermutated()) {
81 * for (int i = c.getFrom(); i < c.getTo(); ++i) {
82 * //permutate
83 * }
84 * } else if (c.wasUpdated()) {
85 * //update item
86 * } else {
87 * for (Item remitem : c.getRemoved()) {
88 * remitem.remove(Outer.this);
89 * }
90 * for (Item additem : c.getAddedSubList()) {
91 * additem.add(Outer.this);
92 * }
93 * }
94 * }
95 * });
96 *
97 * }</pre></blockquote>
98 * <p>
99 * <b>Warning:</b> This class directly accesses the source list to acquire information about the changes.
100 * <br> This effectively makes the Change object invalid when another change occurs on the list.
101 * <br> For this reason it is <b>not safe to use this class on a different thread</b>.
102 * <br> It also means <b>the source list cannot be modified inside the listener</b> since that would invalidate this Change object
103 * for all subsequent listeners.
104 * <p>
105 * Note: in case the change contains multiple changes of different type, these changes must be in the following order:
106 * <em> permutation change(s), add or remove changes, update changes </em>
107 * This is because permutation changes cannot go after add/remove changes as they would change the position of added elements.
108 * And on the other hand, update changes must go after add/remove changes because they refer with their indexes to the current
109 * state of the list, which means with all add/remove changes applied.
110 * @param <E> the list element type
111 * @since JavaFX 2.0
112 */
113 public abstract static class Change<E> {
114 private final ObservableList<E> list;
115
116 /**
117 * Goes to the next change.
118 * The Change instance, in its initial state, is invalid and requires a call to {@code next()} before
119 * calling other methods. The first {@code next()} call will make this object
120 * represent the first change.
121 * @return true if switched to the next change, false if this is the last change.
122 */
123 public abstract boolean next();
124
125 /**
126 * Resets to the initial stage. After this call, {@link #next()} must be called
127 * before working with the first change.
128 */
129 public abstract void reset();
130
131 /**
132 * Constructs a new Change instance on the given list.
133 * @param list The list that was changed
134 */
135 public Change(ObservableList<E> list) {
136 this.list = list;
137 }
138
139 /**
140 * The source list of the change.
141 * @return a list that was changed
142 */
143 public ObservableList<E> getList() {
144 return list;
145 }
146
147 /**
148 * If {@link #wasAdded()} is true, the interval contains all the values that were added.
149 * If {@link #wasPermutated()} is true, the interval marks the values that were permutated.
150 * If {@link #wasRemoved()} is true and {@code wasAdded} is false, {@link #getFrom()} and {@link #getTo()}
151 * should return the same number - the place where the removed elements were positioned in the list.
152 * @return a beginning (inclusive) of an interval related to the change
153 * @throws IllegalStateException if this Change instance is in initial state
154 */
155 public abstract int getFrom();
156
157 /**
158 * The end of the change interval.
159 * @return an end (exclusive) of an interval related to the change.
160 * @throws IllegalStateException if this Change instance is in initial state
161 * @see #getFrom()
162 */
163 public abstract int getTo();
164
165 /**
166 * An immutable list of removed/replaced elements. If no elements
167 * were removed from the list, an empty list is returned.
168 * @return a list with all the removed elements
169 * @throws IllegalStateException if this Change instance is in initial state
170 */
171 public abstract List<E> getRemoved();
172
173 /**
174 * Indicates if the change was only a permutation.
175 * @return true if the change was just a permutation.
176 * @throws IllegalStateException if this Change instance is in initial state
177 */
178 public boolean wasPermutated() {
179 return getPermutation().length != 0;
180 }
181
182 /**
183 * Indicates if elements were added during this change.
184 * @return true if something was added to the list
185 * @throws IllegalStateException if this Change instance is in initial state
186 */
187 public boolean wasAdded() {
188 return !wasPermutated() && !wasUpdated() && getFrom() < getTo();
189 }
190
191 /**
192 * Indicates if elements were removed during this change.
193 * Note that using set will also produce a change with {@code wasRemoved()} returning
194 * true. See {@link #wasReplaced()}.
195 * @return true if something was removed from the list
196 * @throws IllegalStateException if this Change instance is in initial state
197 */
198 public boolean wasRemoved() {
199 return !getRemoved().isEmpty();
200 }
201
202 /**
203 * Indicates if elements were replaced during this change.
204 * This is usually true when set is called on the list.
205 * Set operation will act like remove and add operation at the same time.
206 * <p>
207 * Usually, it's not necessary to use this method directly.
208 * Handling remove operation and then add operation, as in the example in
209 * the {@link Change} class javadoc, will effectively handle the set operation.
210 *
211 * @return same as {@code wasAdded() && wasRemoved()}
212 * @throws IllegalStateException if this Change instance is in initial state
213 */
214 public boolean wasReplaced() {
215 return wasAdded() && wasRemoved();
216 }
217
218 /**
219 * Indicates that the elements between {@link #getFrom()} (inclusive)
220 * to {@link #getTo()} exclusive has changed.
221 * This is the only optional event type and may not be
222 * fired by all ObservableLists.
223 * @return true if the current change is an update change.
224 * @since JavaFX 2.1
225 */
226 public boolean wasUpdated() {
227 return false;
228 }
229
230 /**
231 * Returns a subList view of the list that contains only the elements added. This is actually a shortcut to
232 * <code>c.getList().subList(c.getFrom(), c.getTo());</code>
233 *
234 * <pre>{@code
235 * for (Node n : change.getAddedSubList()) {
236 * // do something
237 * }
238 * }</pre>
239 * @return the newly created sublist view that contains all the added elements.
240 * @throws IllegalStateException if this Change instance is in initial state
241 */
242 public List<E> getAddedSubList() {
243 return wasAdded()? getList().subList(getFrom(), getTo()) : Collections.<E>emptyList();
244 }
245
246 /**
247 * Returns the size of {@link #getRemoved()} list.
248 * @return the number of removed items
249 * @throws IllegalStateException if this Change instance is in initial state
250 */
251 public int getRemovedSize() {
252 return getRemoved().size();
253 }
254
255 /**
256 * Returns the size of the interval that was added.
257 * @return the number of added items
258 * @throws IllegalStateException if this Change instance is in initial state
259 */
260 public int getAddedSize() {
261 return wasAdded() ? getTo() - getFrom() : 0;
262 }
263
264 /**
265 * If this change is a permutation, it returns an integer array
266 * that describes the permutation.
267 * This array maps directly from the previous indexes to the new ones.
268 * This method is not publicly accessible and therefore can return an array safely.
269 * The 0 index of the array corresponds to index {@link #getFrom()} of the list. The same applies
270 * for the last index and {@link #getTo()}.
271 * The method is used by {@link #wasPermutated() } and {@link #getPermutation(int)} methods.
272 * @return empty array if this is not permutation or an integer array containing the permutation
273 * @throws IllegalStateException if this Change instance is in initial state
274 */
275 protected abstract int[] getPermutation();
276
277 /**
278 * This method allows developers to observe the permutations that occurred in this change. In order to get the
279 * new position of an element, you must call:
280 * <pre>
281 * change.getPermutation(oldIndex);
282 * </pre>
283 *
284 * Note: default implementation of this method takes the information
285 * from {@link #getPermutation()} method. You don't have to override this method.
286 * @param i the old index that contained the element prior to this change
287 * @throws IndexOutOfBoundsException if i is out of the bounds of the list
288 * @throws IllegalStateException if this is not a permutation change
289 * @return the new index of the same element
290 */
291 public int getPermutation(int i) {
292 if (!wasPermutated()) {
293 throw new IllegalStateException("Not a permutation change");
294 }
295 return getPermutation()[i - getFrom()];
296 }
297
298 }
299 /**
300 * Called after a change has been made to an ObservableList.
301 *
302 * @param c an object representing the change that was done
303 * @see Change
304 */
305 public void onChanged(Change<? extends E> c);
306 }