1 ///////////////////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
3 // Copyright (C) 2001-2026 the original author or authors.
4 //
5 // This library is free software; you can redistribute it and/or
6 // modify it under the terms of the GNU Lesser General Public
7 // License as published by the Free Software Foundation; either
8 // version 2.1 of the License, or (at your option) any later version.
9 //
10 // This library is distributed in the hope that it will be useful,
11 // but WITHOUT ANY WARRANTY; without even the implied warranty of
12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 // Lesser General Public License for more details.
14 //
15 // You should have received a copy of the GNU Lesser General Public
16 // License along with this library; if not, write to the Free Software
17 // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18 ///////////////////////////////////////////////////////////////////////////////////////////////
19
20 package com.puppycrawl.tools.checkstyle.utils;
21
22 import java.lang.ref.WeakReference;
23
24 /**
25 * A wrapper class for {@link WeakReference} that provides a convenient way
26 * to manage weak references to objects.
27 *
28 * <p>
29 * This class encapsulates the creation and retrieval of weak references,
30 * simplifying the common pattern of storing and accessing weakly referenced objects.
31 * </p>
32 *
33 * @param <T> the type of the referenced object
34 */
35 public final class WeakReferenceHolder<T> {
36
37 /** The weak reference to the object. */
38 private WeakReference<T> reference;
39
40 /**
41 * Constructs a new {@code WeakReferenceHolder} with no initial reference.
42 */
43 public WeakReferenceHolder() {
44 reference = new WeakReference<>(null);
45 }
46
47 /**
48 * Returns the object held by this weak reference, or {@code null} if
49 * the object has been garbage collected.
50 *
51 * @return the referenced object, or {@code null} if it has been collected
52 */
53 public T get() {
54 return reference.get();
55 }
56
57 /**
58 * Updates the referenced object only if the new object is different
59 * from the currently referenced object. After updating, runs the
60 * specified callback if provided.
61 *
62 * @param newObject the new object to reference;
63 * @param afterUpdate a callback to run after updating the reference;
64 */
65 public void lazyUpdate(T newObject, Runnable afterUpdate) {
66 final T previous = reference.get();
67 if (previous != newObject) {
68 reference = new WeakReference<>(newObject);
69 afterUpdate.run();
70 }
71 }
72
73 }