001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2026 the original author or authors.
004//
005// This library is free software; you can redistribute it and/or
006// modify it under the terms of the GNU Lesser General Public
007// License as published by the Free Software Foundation; either
008// version 2.1 of the License, or (at your option) any later version.
009//
010// This library is distributed in the hope that it will be useful,
011// but WITHOUT ANY WARRANTY; without even the implied warranty of
012// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
013// Lesser General Public License for more details.
014//
015// You should have received a copy of the GNU Lesser General Public
016// License along with this library; if not, write to the Free Software
017// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
018///////////////////////////////////////////////////////////////////////////////////////////////
019
020package com.puppycrawl.tools.checkstyle.utils;
021
022import java.lang.ref.WeakReference;
023
024/**
025 * A wrapper class for {@link WeakReference} that provides a convenient way
026 * to manage weak references to objects.
027 *
028 * <p>
029 * This class encapsulates the creation and retrieval of weak references,
030 * simplifying the common pattern of storing and accessing weakly referenced objects.
031 * </p>
032 *
033 * @param <T> the type of the referenced object
034 */
035public final class WeakReferenceHolder<T> {
036
037    /** The weak reference to the object. */
038    private WeakReference<T> reference;
039
040    /**
041     * Constructs a new {@code WeakReferenceHolder} with no initial reference.
042     */
043    public WeakReferenceHolder() {
044        reference = new WeakReference<>(null);
045    }
046
047    /**
048     * Returns the object held by this weak reference, or {@code null} if
049     * the object has been garbage collected.
050     *
051     * @return the referenced object, or {@code null} if it has been collected
052     */
053    public T get() {
054        return reference.get();
055    }
056
057    /**
058     * Updates the referenced object only if the new object is different
059     * from the currently referenced object. After updating, runs the
060     * specified callback if provided.
061     *
062     * @param newObject the new object to reference;
063     * @param afterUpdate a callback to run after updating the reference;
064     */
065    public void lazyUpdate(T newObject, Runnable afterUpdate) {
066        final T previous = reference.get();
067        if (previous != newObject) {
068            reference = new WeakReference<>(newObject);
069            afterUpdate.run();
070        }
071    }
072
073}