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8187443: Forest Consolidation: Move files to unified layout

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Reviewed-by: darcy, ihse
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Erik Joelsson 2017-09-12 19:03:39 +02:00
parent 270fe13182
commit 3789983e89
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src/java.base/share/classes/java/lang/doc-files/ValueBased.html Normal file
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<!doctype html>
<html lang="en">
<head>
<title>Value-based Classes</title>
<link rel="stylesheet" type="text/css" href="../../../stylesheet.css" title="Style">
</head>
<body>
<h2 id="ValueBased">Value-based Classes</h2>
Some classes, such as <code>java.util.Optional</code> and
<code>java.time.LocalDateTime</code>, are <em>value-based</em>. Instances of a
value-based class:
<ul>
<li>are final and immutable (though may contain references to mutable
objects);</li>
<li>have implementations of <code>equals</code>,
<code>hashCode</code>, and <code>toString</code> which are computed
solely from the instance's state and not from its identity or the state
of any other object or variable;</li>
<li>make no use of identity-sensitive operations such as reference
equality (<code>==</code>) between instances, identity hash code of
instances, or synchronization on an instances's intrinsic lock;</li>
<li>are considered equal solely based on <code>equals()</code>, not
based on reference equality (<code>==</code>);</li>
<li>do not have accessible constructors, but are instead instantiated
through factory methods which make no committment as to the identity
of returned instances;</li>
<li>are <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> in any computation or method
invocation should produce no visible change in behavior.
</li>
</ul>
<p>A program may produce unpredictable results if it attempts to distinguish two
references to equal values of a value-based class, whether directly via reference
equality or indirectly via an appeal to synchronization, identity hashing,
serialization, or any other identity-sensitive mechanism. Use of such
identity-sensitive operations on instances of value-based classes may have
unpredictable effects and should be avoided.</p>
</body>
</html>