Draft specification for java.lang.Record

Thu Aug 15 17:15:40 UTC 2019

Hello!

>a private static field corresponding to each component

Final instead of static?

With best regards,
Tagir Valeev

пт, 16 авг. 2019 г., 0:06 Brian Goetz <brian.goetz at oracle.com>:

> 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 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();
> }
>
>
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