1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   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.
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  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).
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  17  * You should have received a copy of the GNU General Public License version
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  23  * questions.
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  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 a changes done to an Observablelist.
  43      * The Change may consist of one or more actual changes and must be iterated by {@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;tem&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      *
  98      * }</pre></blockquote>
  99      * <p>
 100      * <b>Warning:</b> This class directly accesses the source list to acquire information about the changes.
 101      * <br> This effectively makes the Change object invalid when another change occurs on the list.
 102      * <br> For this reason it is <b>not safe to use this class on a different thread</b>.
 103      * <br> It also means <b>the source list cannot be modified inside the listener</b> since that would invalidate this Change object
 104      * for all subsequent listeners.
 105      * <p>
 106      * Note: in case the change contains multiple changes of different type, these changes must be in the following order:
 107      * <em> permutation change(s), add or remove changes, update changes </em>
 108      * This is because permutation changes cannot go after add/remove changes as they would change the position of added elements.
 109      * And on the other hand, update changes must go after add/remove changes because they refer with their indexes to the current
 110      * state of the list, which means with all add/remove changes applied.
 111      * @param <E> the list element type
 112      * @since JavaFX 2.0
 113      */
 114     public abstract static class Change<E> {
 115         private final ObservableList<E> list;
 116 
 117         /**
 118          * Go to the next change.
 119          * The Change in the initial state is invalid a requires a call to next() before
 120          * calling other methods. The first next() call will make this object
 121          * represent the first change.
 122          * @return true if switched to the next change, false if this is the last change.
 123          */
 124         public abstract boolean next();
 125 
 126         /**
 127          * Reset to the initial stage. After this call, the next() must be called
 128          * before working with the first change.
 129          */
 130         public abstract void reset();
 131 
 132         /**
 133          * Constructs a new change done to a list.
 134          * @param list that was changed
 135          */
 136         public Change(ObservableList<E> list) {
 137             this.list = list;
 138         }
 139 
 140         /**
 141          * The source list of the change.
 142          * @return a list that was changed
 143          */
 144         public ObservableList<E> getList() {
 145             return list;
 146         }
 147 
 148         /**
 149          * If wasAdded is true, the interval contains all the values that were added.
 150          * If wasPermutated is true, the interval marks the values that were permutated.
 151          * If wasRemoved is true and wasAdded is false, getFrom() and getTo() should
 152          * return the same number - the place where the removed elements were positioned in the list.
 153          * @return a beginning (inclusive) of an interval related to the change
 154          * @throws IllegalStateException if this Change is in initial state
 155          */
 156         public abstract int getFrom();
 157         /**
 158          * The end of the change interval.
 159          * @return a end (exclusive) of an interval related to the change.
 160          * @throws IllegalStateException if this Change is in initial state
 161          * @see #getFrom()
 162          */
 163         public abstract int getTo();
 164         /**
 165          * An immutable list of removed/replaced elements. If no elements
 166          * were removed from the list, an empty list is returned.
 167          * @return a list with all the removed elements
 168          * @throws IllegalStateException if this Change is in initial state
 169          */
 170         public abstract List<E> getRemoved();
 171         /**
 172          * Indicates if the change was only a permutation.
 173          * @return true if the change was just a permutation.
 174          * @throws IllegalStateException if this Change is in initial state
 175          */
 176         public boolean wasPermutated() {
 177             return getPermutation().length != 0;
 178         }
 179 
 180         /**
 181          * Indicates if elements were added during this change
 182          * @return true if something was added to the list
 183          * @throws IllegalStateException if this Change is in initial state
 184          */
 185         public boolean wasAdded() {
 186             return !wasPermutated() && !wasUpdated() && getFrom() < getTo();
 187         }
 188 
 189         /**
 190          * Indicates if elements were removed during this change.
 191          * Note that using set will also produce a change with wasRemoved() returning
 192          * true. See {@link #wasReplaced()}.
 193          * @return true if something was removed from the list
 194          * @throws IllegalStateException if this Change is in initial state
 195          */
 196         public boolean wasRemoved() {
 197             return !getRemoved().isEmpty();
 198         }
 199 
 200         /**
 201          * Indicates if elements were replaced during this change.
 202          * This is usually true when set is called on the list.
 203          * Set operation will act like remove and add operation at the same time.
 204          * <p>
 205          * Usually, it's not necessary to use this method directly.
 206          * Handling remove operation and then add operation, as in the example {@link ListChangeListener$Change above},
 207          * will effectively handle also set operation.
 208          *
 209          * @return same <code> as wasAdded() && wasRemoved() </code>
 210          * @throws IllegalStateException if this Change is in initial state
 211          */
 212         public boolean wasReplaced() {
 213             return wasAdded() && wasRemoved();
 214         }
 215 
 216         /**
 217          * Indicates that the elements between getFrom() (inclusive)
 218          * to getTo() exclusive has changed.
 219          * This is the only optional event type and may not be
 220          * fired by all ObservableLists.
 221          * @return true if the current change is an update change.
 222          * @since JavaFX 2.1
 223          */
 224         public boolean wasUpdated() {
 225             return false;
 226         }
 227 
 228         /**
 229          * To get a subList view of the list that contains only the elements
 230          * added, use getAddedSubList() method.
 231          * This is actually a shortcut to <code>c.getList().subList(c.getFrom(), c.getTo());</code><br>
 232          *
 233          * <pre><code>
 234          * for (Node n : change.getAddedSubList()) {
 235          *       // do something
 236          * }
 237          * </code></pre>
 238          * @return the newly created sublist view that contains all the added elements.
 239          * @throws IllegalStateException if this Change is in initial state
 240          */
 241         public List<E> getAddedSubList() {
 242             return wasAdded()? getList().subList(getFrom(), getTo()) : Collections.<E>emptyList();
 243         }
 244 
 245         /**
 246          * Size of getRemoved() list.
 247          * @return the number of removed items
 248          * @throws IllegalStateException if this Change is in initial state
 249          */
 250         public int getRemovedSize() {
 251             return getRemoved().size();
 252         }
 253 
 254         /**
 255          * Size of the interval that was added.
 256          * @return the number of added items
 257          * @throws IllegalStateException if this Change is in initial state
 258          */
 259         public int getAddedSize() {
 260             return wasAdded() ? getTo() - getFrom() : 0;
 261         }
 262 
 263         /**
 264          * If this change is an permutation, it returns an integer array
 265          * that describes the permutation.
 266          * This array maps directly from the previous indexes to the new ones.
 267          * This method is not publicly accessible and therefore can return an array safely.
 268          * The 0 index of the array corresponds to index {@link #getFrom()} of the list. The same applies
 269          * for the last index and {@link #getTo()}.
 270          * The method is used by {@link #wasPermutated() } and {@link #getPermutation(int)} methods.
 271          * @return empty array if this is not permutation or an integer array containing the permutation
 272          * @throws IllegalStateException if this Change is in initial state
 273          */
 274         protected abstract int[] getPermutation();
 275 
 276         /**
 277          * By calling these method, you can observe the permutation that happened.
 278          * In order to get the new position of an element, you must call:
 279          * <pre>
 280          *    change.getPermutation(oldIndex);
 281          * </pre>
 282          *
 283          * Note: default implementation of this method takes the information
 284          * from {@link #getPermutation()} method. You don't have to override this method.
 285          * @param i the old index that contained the element prior to this change
 286          * @throws IndexOutOfBoundsException if i is out of the bounds of the list
 287          * @throws IllegalStateException if this is not a permutation change
 288          * @return the new index of the same element
 289          */
 290         public int getPermutation(int i) {
 291             if (!wasPermutated()) {
 292                 throw new IllegalStateException("Not a permutation change");
 293             }
 294             return getPermutation()[i - getFrom()];
 295         }
 296 
 297     }
 298     /**
 299      * Called after a change has been made to an ObservableList.
 300      *
 301      * @param c an object representing the change that was done
 302      * @see Change
 303      */
 304     public void onChanged(Change<? extends E> c);
 305 }