Hi all, why Record is a class (an abstract class) and not an interface ? It's not like j.l.Enum which has two fields and several method implementations, Record just strengthen the contract of Object like a Set strengthen the contract of Collection, so it seems more like an interface to me.
Being an interface also means that we will be able to mix an inline type and a record, an inline record?, for free, and more generally Record being an interface is less disruptive than being a class when you want to retrofit a class to be a record. Rémi > De: "Brian Goetz" <brian.go...@oracle.com> > À: "amber-spec-experts" <amber-spec-experts@openjdk.java.net> > Envoyé: Jeudi 15 Août 2019 19:06:02 > Objet: Draft specification for java.lang.Record > Draft spec, please comment. > /* * 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 [ http://www.oracle.com/ | 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(); > }
