src/java.base/share/classes/java/lang/reflect/doc-files/MutationMethods.html - master - wstartsev/jdk

src/java.base/share/classes/java/lang/reflect/doc-files/MutationMethods.html
68 строк3 KB
Alan Bateman
8353835: Implement JEP 500: Prepare to Make Final Mean Final
18 ноя 2025, 11:06
18 ноя 2025, 11:0626460b6
<!doctype html>
<!--
 Copyright (c) 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.
-->
<html lang="en">
<head>
    <title>Mutation methods</title>
</head>
<body>

<h1 id="mutation">Mutation methods</h1>

<p>A number of methods in Java SE API provide <em>write</em> access to non-static
final fields. This means that Java code can alter the value of a final field
after the field has been initialized in a constructor.

The methods that provide write access, known as <em>mutation methods</em> are:
<ul>
    <li>{@link java.lang.reflect.Field#set(Object, Object)}</li>
    <li>{@link java.lang.reflect.Field#setBoolean(Object, boolean)}</li>
    <li>{@link java.lang.reflect.Field#setByte(Object, byte)}</li>
    <li>{@link java.lang.reflect.Field#setChar(Object, char)}</li>
    <li>{@link java.lang.reflect.Field#setInt(Object, int)}</li>
    <li>{@link java.lang.reflect.Field#setLong(Object, long)}</li>
    <li>{@link java.lang.reflect.Field#setFloat(Object, float)}</li>
    <li>{@link java.lang.reflect.Field#setDouble(Object, double)}</li>
    <li>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter(java.lang.reflect.Field)}</li>
</ul>

<p> The use of mutation methods to alter the values of final fields is
strongly inadvisable because it undermines the correctness of programs written in
expectation of final fields being immutable.

<p> In the reference implementation, a module can be granted the capability to mutate
final instance fields of classes in packages that are open to the module using
the command line option <code>--enable-final-field-mutation=M1,M2, ... Mn}</code> where
<code>M1</code>, <code>M2</code>, <code>...Mn</code> are module names (for the unnamed
module, the special value <code>ALL-UNNAMED</code> can be used). Mutation of final
instance fields of classes from modules not listed by that option is deemed
<em>illegal</em>.
The command line option <code>--illegal-final-field-mutation</code> controls how illegal
final mutation is handled. Valid values for this command line option are "warn", "allow",
"debug, and "deny".  If this option is not specified then the default is "warn" so that
illegal final field mutation will result in a warning at runtime.

</body>
</html>