What methods should go into a java.util.Objects class in JDK 7?

[David Holmes - Sun Microsystems]

Hi Joe,

I thought the point that Jason Mehrens was making was that this:

+    public static String toString(Object o) {
+        String.valueOf(o);
+    }

is actually pointless. Why introduce such redundancy when people can 
just use String.valueOf directly ? This doesn't provide any benefit.

PS. It should be "return String.valueOf(o);" of course.

David Holmes

Joe Darcy said the following on 10/07/09 08:50:
> Joe Darcy wrote:
>> Joe Darcy wrote:
>>> Joe Darcy wrote:
>>>> Stephen Colebourne wrote:
>>>>> Joe Darcy wrote:
>>>>>> What other utility methods would have broad enough use and 
>>>>>> applicability to go into a common java.util class?
>>>>>
>>>>> Joe,
>>>>> You've asked for a call for ideas, but not given any indication of 
>>>>> process. Are you going to evaluate everything that comes in and 
>>>>> pick the best a la Coin? Or allow anyone to send in patches? 
>>>>
>>>> Those options are not mutually exclusive; patches are welcome 
>>>> subject to the usual terms and conditions.
>>>>
>>>>> Who decides what is in and what is out?
>>>>
>>>> This is a little side project of mine and I wanted to get some 
>>>> feedback before preparing a formal change for review, possibly 
>>>> including patches from others.
>>>>
>>>> -Joe
>>>
>>> I'm getting caught up after the JVM Languages Summit and will post 
>>> some java.util.Objects code for review in the near future.
>>>
>>> -Joe
>>
>> Below is a patch implementing the methods I think should go into 
>> java.util.Objects as a first cut:
>>
>> * null safe two-argument equals method
>> * null safe hashCode(Object) returning 0 for null
>> * null safe toString(Object), returning "null" for a null argument
>> * null tolerating compare method; tests if both arguments are == and 
>> if not calls compare
>>
>> The need for the last of these in Objects isn't quite as clear.
>>
>> Var-arg-ifying some of the existing methods in Arrays, 
>> (hashCode(Object[]), deepHashCode(Object[]) and toString(Object[])), 
>> is probably worthwhile but can be done separately.
>>
>> I wouldn't oppose a toDebugString(Object) method going into the 
>> platform somewhere, but I don't think it necessarily belongs in Objects.
>>
>> Further below is the code for an annotation processor which finds 
>> candidate equals methods to be replaced with Objects.equals.  It found 
>> over half a dozen good candidates in the jdk repository.  To run the 
>> annotation processor, first compile the class and then run it with 
>> javac similar to this:
>>
>> javac -proc:only -processor EqualsFinder -processorpath <path to 
>> processor> sources
>>
>> -Joe
>>
> 
> Updated patch of java.util.Objects with some spec clarifications 
> suggested by Alan Bateman and the use of and reference to 
> String.valueOf(Object) observed by Jason Mehrens.
> 
> -Joe
> 
> 
> --- /dev/null    2009-08-12 17:12:33.000000000 -0700
> +++ new/src/share/classes/java/util/Objects.java    2009-10-06 
> 15:47:16.000000000 -0700
> @@ -0,0 +1,100 @@
> +/*
> + * Copyright 2009 Sun Microsystems, Inc.  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.  Sun designates this
> + * particular file as subject to the "Classpath" exception as provided
> + * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa 
> Clara,
> + * CA 95054 USA or visit www.sun.com if you need additional information or
> + * have any questions.
> + */
> +
> +package java.util;
> +
> +/**
> + * This class consists of {@code static} utility methods for operating
> + * on objects.
> + *
> + * @since 1.7
> + */
> +public class Objects {
> +    private Objects() {
> +        throw new AssertionError("No java.util.Objects instances for 
> you!");
> +    }
> +
> +    /**
> +     * Returns {@code true} if the arguments are equal to each other
> +     * and {@code false} otherwise.
> +     * Consequently, if both arguments are {@code null}, {@code true}
> +     * is returned and if exactly one argument is {@code null}, {@code
> +     * false} is returned.  Otherwise, equality is determined by using
> +     * the {@link Object#equals equals} method of the first
> +     * argument.
> +     *
> +     * @return {@code true} if the arguments are equal to each other
> +     * and {@code false} otherwise
> +     * @see Object#equals(Object)
> +     */
> +    public static boolean equals(Object a, Object b) {
> +        return (a == b) || (a != null && a.equals(b));
> +    }
> +
> +    /**
> +     * Returns the hash code of a non-{@code null} argument and 0 for
> +     * a {@code null} argument.
> +     *
> +     * @return the hash code of a non-{@code null} argument and 0 for
> +     * a {@code null} argument
> +     * @see Object#hashCode
> +     */
> +    public static int hashCode(Object o) {
> +        return o != null ? o.hashCode() : 0;
> +    }
> +
> +    /**
> +     * Returns the result of calling {@code toString} for a non-{@code
> +     * null} argument and {@code "null"} for a {@code null} argument.
> +     *
> +     * @return the result of calling {@code toString} for a non-{@code
> +     * null} argument and {@code "null"} for a {@code null} argument
> +     * @see Object#toString
> +     * @see String#valueOf(Object)
> +     */
> +    public static String toString(Object o) {
> +        String.valueOf(o);
> +    }
> +
> +    /**
> +     * Returns 0 if the arguments are identical and {@code
> +     * c.compare(a, b)} otherwise.
> +     * Consequently, if both arguments are {@code null} 0
> +     * is returned.
> +     *
> +     * <p>Note that if one of the argument is {@code null}, a {@code
> +     * NullPointerException} may or may not be thrown depending on
> +     * what ordering policy, if any, the {@link Comparator Comparator}
> +     * chooses to have for {@code null} values.
> +     *
> +     * @return 0 if the arguments are identical and {@code
> +     * c.compare(a, b)} otherwise.
> +     * @see Comparable
> +     * @see Comparator
> +     */
> +    public static <T> int compare(T a, T b, Comparator<? super T> c) {
> +        return (a == b) ? 0 :  c.compare(a, b);
> +    }
> +}