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

src/java.base/share/classes/java/lang/doc-files/ValueBased.html
72 строки4 KB
Nizar Benalla
8336259: Wrong link to stylesheet.css in JavaDoc API documentation
13 июл 2024, 00:50
13 июл 2024, 00:505bc86f3
<!doctype html>
<!--
 Copyright (c) 2013, 2024, 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>Value-based Classes</title>
</head>
<body>
<h1 id="ValueBased">{@index "Value-based Classes"}</h1>

Some classes, such as <code>java.lang.Integer</code> and
<code>java.time.LocalDate</code>, are <em>value-based</em>.
A value-based class has the following properties:
<ul>
    <li>the class declares only final instance fields (though these may contain references
        to mutable objects);</li>
    <li>the class's implementations of <code>equals</code>, <code>hashCode</code>,
        and <code>toString</code> compute their results solely from the values
        of the class's instance fields (and the members of the objects they
        reference), not from the instance's identity;</li>
    <li>the class's methods treat instances as <em>freely substitutable</em>
        when equal, meaning that interchanging any two instances <code>x</code> and
        <code>y</code> that are equal according to <code>equals()</code> produces no
        visible change in the behavior of the class's methods;</li>
    <li>the class performs no synchronization using an instance's monitor;</li>
    <li>the class does not declare (or has deprecated any) accessible constructors;</li>
    <li>the class does not provide any instance creation mechanism that promises
        a unique identity on each method call&mdash;in particular, any factory
        method's contract must allow for the possibility that if two independently-produced
        instances are equal according to <code>equals()</code>, they may also be
        equal according to <code>==</code>;</li>
    <li>the class is final, and extends either <code>Object</code> or a hierarchy of
        abstract classes that declare no instance fields or instance initializers
        and whose constructors are empty.</li>
</ul>

<p>When two instances of a value-based class are equal (according to `equals`), a program
    should not attempt to distinguish between their identities, whether directly via reference
    equality or indirectly via an appeal to synchronization, identity hashing,
    serialization, or any other identity-sensitive mechanism.</p>

<p>Synchronization on instances of value-based classes is strongly discouraged,
    because the programmer cannot guarantee exclusive ownership of the
    associated monitor.</p>

<p>Identity-related behavior of value-based classes may change in a future release.
    For example, synchronization may fail.</p>

</body>
</html>