Java tutorial
/* * Copyright (c) 2010, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package javafx.collections; import java.util.Collections; import java.util.List; /** * Interface that receives notifications of changes to an ObservableList. * * @param <E> the list element type * @see Change * @since JavaFX 2.0 */ @FunctionalInterface public interface ListChangeListener<E> { /** * Represents a report of changes done to an {@link ObservableList}. The change may consist of one or more actual * changes and must be iterated by calling the {@link #next()} method. * * Each change must be one of the following: * <ul> * <li><b>Permutation change</b> : {@link #wasPermutated()} returns true in this case. * The permutation happened at range between {@link #getFrom() from} (inclusive) and {@link #getTo() to} (exclusive) and * can be queried by calling {@link #getPermutation(int)} method. * <li><b>Add or remove change</b> : In this case, at least one of the {@link #wasAdded()}, {@link #wasRemoved()} returns true. * If both methods return true, {@link #wasReplaced()} will also return true. * <p>The {@link #getRemoved()} method returns a list of elements that have been * replaced or removed from the list. * <p> The range between {@link #getFrom() from} (inclusive) and {@link #getTo() to} (exclusive) * denotes the sublist of the list that contain new elements. Note that this is a half-open * interval, so if no elements were added, {@code getFrom()} is equal to {@code getTo()}. * <p>It is possible to get a list of added elements by calling getAddedSubList(). * <p>Note that in order to maintain correct indexes of the separate add/remove changes, these changes * <b>must</b> be sorted by their {@code from} index. * <li><b>Update change</b> : {@link #wasUpdated()} return true on an update change. * All elements between {@link #getFrom() from} (inclusive) and {@link #getTo() to} (exclusive) were updated. * </ul> * * <b>Important:</b> It's necessary to call {@link #next()} method before calling * any other method of {@code Change}. The same applies after calling {@link #reset()}. * The only methods that works at any time is {@link #getList()}. * *<p> * Typical usage is to observe changes on an ObservableList in order * to hook or unhook (or add or remove a listener) or in order to maintain * some invariant on every element in that ObservableList. A common code * pattern for doing this looks something like the following:<br> * * <blockquote><pre> * ObservableList<Item> theList = ...; * * theList.addListener(new ListChangeListener<Item>() { * public void onChanged(Change<Item> c) { * while (c.next()) { * if (c.wasPermutated()) { * for (int i = c.getFrom(); i < c.getTo(); ++i) { * //permutate * } * } else if (c.wasUpdated()) { * //update item * } else { * for (Item remitem : c.getRemoved()) { * remitem.remove(Outer.this); * } * for (Item additem : c.getAddedSubList()) { * additem.add(Outer.this); * } * } * } * }); * * }</pre></blockquote> * <p> * <b>Warning:</b> This class directly accesses the source list to acquire information about the changes. * <br> This effectively makes the Change object invalid when another change occurs on the list. * <br> For this reason it is <b>not safe to use this class on a different thread</b>. * <br> It also means <b>the source list cannot be modified inside the listener</b> since that would invalidate this Change object * for all subsequent listeners. * <p> * Note: in case the change contains multiple changes of different type, these changes must be in the following order: * <em> permutation change(s), add or remove changes, update changes </em> * This is because permutation changes cannot go after add/remove changes as they would change the position of added elements. * And on the other hand, update changes must go after add/remove changes because they refer with their indexes to the current * state of the list, which means with all add/remove changes applied. * @param <E> the list element type * @since JavaFX 2.0 */ public abstract static class Change<E> { private final ObservableList<E> list; /** * Goes to the next change. * The Change instance, in its initial state, is invalid and requires a call to {@code next()} before * calling other methods. The first {@code next()} call will make this object * represent the first change. * @return true if switched to the next change, false if this is the last change. */ public abstract boolean next(); /** * Resets to the initial stage. After this call, {@link #next()} must be called * before working with the first change. */ public abstract void reset(); /** * Constructs a new Change instance on the given list. * @param list The list that was changed */ public Change(ObservableList<E> list) { this.list = list; } /** * The source list of the change. * @return a list that was changed */ public ObservableList<E> getList() { return list; } /** * If {@link #wasAdded()} is true, the interval contains all the values that were added. * If {@link #wasPermutated()} is true, the interval marks the values that were permutated. * If {@link #wasRemoved()} is true and {@code wasAdded} is false, {@link #getFrom()} and {@link #getTo()} * should return the same number - the place where the removed elements were positioned in the list. * @return a beginning (inclusive) of an interval related to the change * @throws IllegalStateException if this Change instance is in initial state */ public abstract int getFrom(); /** * The end of the change interval. * @return an end (exclusive) of an interval related to the change. * @throws IllegalStateException if this Change instance is in initial state * @see #getFrom() */ public abstract int getTo(); /** * An immutable list of removed/replaced elements. If no elements * were removed from the list, an empty list is returned. * @return a list with all the removed elements * @throws IllegalStateException if this Change instance is in initial state */ public abstract List<E> getRemoved(); /** * Indicates if the change was only a permutation. * @return true if the change was just a permutation. * @throws IllegalStateException if this Change instance is in initial state */ public boolean wasPermutated() { return getPermutation().length != 0; } /** * Indicates if elements were added during this change. * @return true if something was added to the list * @throws IllegalStateException if this Change instance is in initial state */ public boolean wasAdded() { return !wasPermutated() && !wasUpdated() && getFrom() < getTo(); } /** * Indicates if elements were removed during this change. * Note that using set will also produce a change with {@code wasRemoved()} returning * true. See {@link #wasReplaced()}. * @return true if something was removed from the list * @throws IllegalStateException if this Change instance is in initial state */ public boolean wasRemoved() { return !getRemoved().isEmpty(); } /** * Indicates if elements were replaced during this change. * This is usually true when set is called on the list. * Set operation will act like remove and add operation at the same time. * <p> * Usually, it's not necessary to use this method directly. * Handling remove operation and then add operation, as in the example in * the {@link Change} class javadoc, will effectively handle the set operation. * * @return same as {@code wasAdded() && wasRemoved()} * @throws IllegalStateException if this Change instance is in initial state */ public boolean wasReplaced() { return wasAdded() && wasRemoved(); } /** * Indicates that the elements between {@link #getFrom()} (inclusive) * to {@link #getTo()} exclusive has changed. * This is the only optional event type and may not be * fired by all ObservableLists. * @return true if the current change is an update change. * @since JavaFX 2.1 */ public boolean wasUpdated() { return false; } /** * Returns a subList view of the list that contains only the elements added. This is actually a shortcut to * <code>c.getList().subList(c.getFrom(), c.getTo());</code> * * <pre>{@code * for (Node n : change.getAddedSubList()) { * // do something * } * }</pre> * @return the newly created sublist view that contains all the added elements. * @throws IllegalStateException if this Change instance is in initial state */ public List<E> getAddedSubList() { return wasAdded() ? getList().subList(getFrom(), getTo()) : Collections.<E>emptyList(); } /** * Returns the size of {@link #getRemoved()} list. * @return the number of removed items * @throws IllegalStateException if this Change instance is in initial state */ public int getRemovedSize() { return getRemoved().size(); } /** * Returns the size of the interval that was added. * @return the number of added items * @throws IllegalStateException if this Change instance is in initial state */ public int getAddedSize() { return wasAdded() ? getTo() - getFrom() : 0; } /** * If this change is a permutation, it returns an integer array * that describes the permutation. * This array maps directly from the previous indexes to the new ones. * This method is not publicly accessible and therefore can return an array safely. * The 0 index of the array corresponds to index {@link #getFrom()} of the list. The same applies * for the last index and {@link #getTo()}. * The method is used by {@link #wasPermutated() } and {@link #getPermutation(int)} methods. * @return empty array if this is not permutation or an integer array containing the permutation * @throws IllegalStateException if this Change instance is in initial state */ protected abstract int[] getPermutation(); /** * This method allows developers to observe the permutations that occurred in this change. In order to get the * new position of an element, you must call: * <pre> * change.getPermutation(oldIndex); * </pre> * * Note: default implementation of this method takes the information * from {@link #getPermutation()} method. You don't have to override this method. * @param i the old index that contained the element prior to this change * @throws IndexOutOfBoundsException if i is out of the bounds of the list * @throws IllegalStateException if this is not a permutation change * @return the new index of the same element */ public int getPermutation(int i) { if (!wasPermutated()) { throw new IllegalStateException("Not a permutation change"); } return getPermutation()[i - getFrom()]; } } /** * Called after a change has been made to an ObservableList. * * @param c an object representing the change that was done * @see Change */ public void onChanged(Change<? extends E> c); }