It might be worth also saying something about finalization. I think the choices
are to do nothing (be finalizer-agnostic) or to prohibit it. Generating a
finalize() method for every record class seems like a non-starter.
I'm leaning toward prohibiting finalization, for a couple reasons. First,
Object.finalize() is deprecated, and finalization will eventually be removed, so
we'd like to discourage new code from using finalizers. Second, if a
user-provided record constructor throws an exception, the partially-initialized
record instance will be visible to the finalizer and it potentially can be
resurrected. This seems like a really bad idea.
Suggestion:
/**
* Finalization of record class instances is disallowed.
*
* @implSpec
* This method implementation does nothing.
*/
protected final void finalize() { }
s'marks
On 8/15/19 10:34 AM, Brian Goetz wrote:
Re-sending as plain text, since the formatting got mangled by mailers.
/*
* Copyright (c) 2019, 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.
*/
package java.lang;
/**
* This is the common base class of all Java language record classes.
*
* <p>More information about records, including descriptions of the
* implicitly declared methods synthesized by the compiler, can be
* found in section 8.10 of
* <cite>The Java™ Language Specification</cite>.
*
* <p>A <em>record class</em> is a shallowly immutable, transparent carrier for
* a fixed set of values, called the <em>record components</em>. The
Java™
* language provides concise syntax for declaring record classes, whereby the
* record components are declared in the record header. The list of record
* components declared in the record header form the <em>record
descriptor</em>.
*
* <p>A record class has the following mandated members: a public <em>canonical
* constructor</em>, whose descriptor is the same as the record descriptor;
* a private static field corresponding to each component, whose name and
* type are the same as that of the component; a public accessor method
* corresponding to each component, whose name and return type are the same as
* that of the component. If not explicitly declared in the body of the
record,
* implicit implementations for these members are provided.
*
* <p>The implicit declaration of the canonical constructor initializes the
* component fields from the corresponding constructor arguments. The implicit
* declaration of the accessor methods returns the value of the corresponding
* component field. The implicit declaration of the {@link
Object#equals(Object)},
* {@link Object#hashCode()}, and {@link Object#toString()} methods are derived
* from all of the component fields.
*
* <p>The primary reasons to provide an explicit declaration for the
* canonical constructor or accessor methods are to validate constructor
* arguments, perform defensive copies on mutable components, or normalize
groups
* of components (such as reducing a rational number to lowest terms.) If any
* of these are provided explicitly.
*
* <p>For all record classes, the following invariant must hold: if a record
R's
* components are {@code c1, c2, ... cn}, then if a record instance is copied
* as follows:
* <pre>
* R copy = new R(r.c1(), r.c2(), ..., r.cn());
* </pre>
* then it must be the case that {@code r.equals(copy)}.
*
* @jls 8.10
* @since 14
*/
public abstract class Record {
/**
* Indicates whether some other object is "equal to" this one. In addition
* to the general contract of {@link Object#equals(Object)},
* record classes must further participate in the invariant that when
* a record instance is "copied" by passing the result of the record
component
* accessor methods to the canonical constructor, the resulting copy is
* equal to the original instance.
*
* @implNote
* The implicitly provided implementation returns {@code true} if and
* only if the argument is an instance of the same record type as this
object,
* and each component of this record is equal to the corresponding
component
* of the argument, according to {@link Object#equals(Object)} for
components
* whose types are reference types, and {@code ==} for components whose
* types are primitive types.
*
* @see Object#equals(Object)
*
* @param obj the reference object with which to compare.
* @return {@code true} if this object is the same as the obj
* argument; {@code false} otherwise.
*/
@Override
public abstract boolean equals(Object obj);
/**
* {@inheritDoc}
*
* @implNote
* The implicitly provided implementation returns a hash code value derived
* by combining the hash code value for all the components, according to
* {@link Object#hashCode()} for components whose types are reference
types,
* or the primitive wrapper hash code for components whose types are
primitive
* types.
*
* @see Object#hashCode()
*
* @return a hash code value for this object.
*/
@Override
public abstract int hashCode();
/**
* {@inheritDoc}
*
* @implNote
* The implicitly provided implementation returns a string that is derived
* from the name of the record class and the names and string
representations
* of all the components, according to {@link Object#toString()} for
components
* whose types are reference types, and the primitive wrapper {@code
toString}
* method for components whose types are primitive types.
*
* @see Object#toString() ()
*
* @return a string representation of the object.
*/
@Override
public abstract String toString();
}
