WeakReference.java

https://github.com/*
 * Copyright (c) 1997, 2025, 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 java.lang.ref;

import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;

import java.util.Objects;

https://github.com/**
 * Weak reference objects, which do not prevent their referents from being
 * made finalizable, finalized, and then reclaimed.  Weak references are most
 * often used to implement canonicalizing mappings.
 *
 * <div class="preview-block">
 *      <div class="preview-comment">
 *          The referent must have {@linkplain Objects#hasIdentity(Object) object identity}.
 *          When preview features are enabled, attempts to create a reference
 *          to a {@linkplain Class#isValue value object} result in an {@link IdentityException}.
 *      </div>
 * </div>
 *
 * <p> Suppose that the garbage collector determines at a certain point in time
 * that an object is <a href="package-summary.html#reachability">weakly
 * reachable</a>.  At that time it will atomically clear all weak references to
 * that object and all weak references to any other weakly-reachable objects
 * from which that object is reachable through a chain of strong and soft
 * references.  At the same time it will declare all of the formerly
 * weakly-reachable objects to be finalizable.  At the same time or at some
 * later time it will enqueue those newly-cleared weak references that are
 * registered with reference queues.
 * @param <T> the type of the referent
 *
 * @author   Mark Reinhold
 * @since    1.2
 */

@NullMarked
public non-sealed class WeakReference<@jdk.internal.RequiresIdentity T> extends Reference<T> {

    /**
     * Creates a new weak reference that refers to the given object.  The new
     * reference is not registered with any queue.
     *
     * @param referent object the new weak reference will refer to
     * @throws IdentityException if the referent is not an
     *         {@link java.util.Objects#hasIdentity(Object) identity object}
     */
    public WeakReference(@jdk.internal.RequiresIdentity @Nullable T referent) {
        super(referent);
    }

    /**
     * Creates a new weak reference that refers to the given object and is
     * registered with the given queue.
     *
     * @param referent object the new weak reference will refer to
     * @param q the queue with which the reference is to be registered,
     *          or {@code null} if registration is not required
     * @throws IdentityException if the referent is not an
     *         {@link java.util.Objects#hasIdentity(Object) identity object}
     */
    public WeakReference(@jdk.internal.RequiresIdentity @Nullable T referent, @Nullable ReferenceQueue<? super T> q) {
        super(referent, q);
    }

}