1 /*

     2  * Copyright (c) 2012, 2013, 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

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    24  */

    25 

    26 package java.lang.invoke;

    27 

    28 import java.lang.annotation.*;

    29 

    30 /**

    31  * A field may be annotated as stable if all of its component variables

    32  * changes value at most once.

    33  * A field's value counts as its component value.

    34  * If the field is typed as an array, then all the non-null components

    35  * of the array, of depth up to the rank of the field's array type,

    36  * also count as component values.

    37  * By extension, any variable (either array or field) which has annotated

    38  * as stable is called a stable variable, and its non-null or non-zero

    39  * value is called a stable value.

    40  * <p>

    41  * Since all fields begin with a default value of null for references

    42  * (resp., zero for primitives), it follows that this annotation indicates

    43  * that the first non-null (resp., non-zero) value stored in the field

    44  * will never be changed.

    45  * <p>

    46  * If the field is not of an array type, there are no array elements,

    47  * then the value indicated as stable is simply the value of the field.

    48  * If the dynamic type of the field value is an array but the static type

    49  * is not, the components of the array are <em>not</em> regarded as stable.

    50  * <p>

    51  * If the field is an array type, then both the field value and

    52  * all the components of the field value (if the field value is non-null)

    53  * are indicated to be stable.

    54  * If the field type is an array type with rank {@code N > 1},

    55  * then each component of the field value (if the field value is non-null),

    56  * is regarded as a stable array of rank {@code N-1}.

    57  * <p>

    58  * Fields which are declared {@code final} may also be annotated as stable.

    59  * Since final fields already behave as stable values, such an annotation

    60  * indicates no additional information, unless the type of the field is

    61  * an array type.

    62  * <p>

    63  * It is (currently) undefined what happens if a field annotated as stable

    64  * is given a third value.  In practice, if the JVM relies on this annotation

    65  * to promote a field reference to a constant, it may be that the Java memory

    66  * model would appear to be broken, if such a constant (the second value of the field)

    67  * is used as the value of the field even after the field value has changed.

    68  */

    69 /* package-private */

    70 @Target(ElementType.FIELD)

    71 @Retention(RetentionPolicy.RUNTIME)

    72 @interface Stable {

    73 }