1 /*
   2  * Copyright (c) 2010, 2018, 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&lt;Item&gt; theList = ...;
  76      *
  77      * theList.addListener(new ListChangeListener&lt;Item&gt;() {
  78      *     public void onChanged(Change&lt;Item&gt; c) {
  79      *         while (c.next()) {
  80      *             if (c.wasPermutated()) {
  81      *                 for (int i = c.getFrom(); i &lt; 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 }