What methods should go into a java.util.Objects class in JDK 7? (original) (raw)

David Holmes - Sun Microsystems David.Holmes at Sun.COM
Tue Oct 6 23:07:33 UTC 2009

Hi Joe,

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

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 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. + * + *

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 int compare(T a, T b, Comparator<? super T> c) { + return (a == b) ? 0 : c.compare(a, b); + } +}

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