1 /*
 2  * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
 3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 4  *
 5  * This code is free software; you can redistribute it and/or modify it
 6  * under the terms of the GNU General Public License version 2 only, as
 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.
10  *
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).
16  *
17  * You should have received a copy of the GNU General Public License version
18  * 2 along with this work; if not, write to the Free Software Foundation,
19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20  *
21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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24  */
25 
26 package jdk.internal.vm.annotation;
27 
28 import java.lang.annotation.*;
29 
30 /**
31  * A null-restricted field is a field that does not store {@code null}.
32  * The type of the field is expected to be a value class type with the
33  * {@link ImplicitlyConstructible} annotation. The initial value of the field
34  * is the zero instance of the given class, and attempts to write {@code null}
35  * to the field will throw an exception.
36  * <p>
37  * The HotSpot VM uses this annotation to enable flattened encodings for the
38  * field that would otherwise be impossible.
39  * <p>
40  * Because these behaviors are not specified by Java SE, this annotation should
41  * only be used by internal JDK classes for experimental purposes and should not
42  * affect user-observable outcomes.
43  */
44 @Target(ElementType.FIELD)
45 @Retention(RetentionPolicy.RUNTIME)
46 public @interface NullRestricted {
47 }