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

[Joe Darcy]

David Holmes - Sun Microsystems wrote:
> Hi Joe,
>
> I thought the point that Jason Mehrens was making was that this:
>
> +    public static String toString(Object o) {
> +        String.valueOf(o); hat Jason Mehrens was making was that this:
>
> +    public static String toString(Object o) {
> +        String.valueOf(o);
> +    }
>
> is actually pointless. Why introduce
> +    }
>
> is actually pointless. Why introduce such redundancy when people can 
> just use String.valueOf directly ? 

Because, IMO, String.valueOf is obscure and hard to find and from its 
name it is not clear it does null-safe toString on the argument.  For 
example, I didn't know about String.valueOf.  It is much clearer what 
Objects.toString is intended to do.

> This doesn't provide any benefit.

I think having the new method be commonly called would be a benefit :-)

I don't think having a one-line forwarding method in Objects is that 
harmful.

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

Fixed.

Thanks,

-Joe

>
> 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);
>> +    }
>> +}