j.u.Objects follow-up: deepEquals(Object, Object)?

Eamonn McManus Eamonn.McManus at Sun.COM
Fri Oct 9 09:30:33 UTC 2009

Joseph D. Darcy wrote:
 > What are scenarios where this method would be used?

I use a similar method fairly often in unit tests.  JUnit's assertEquals doesn't
do the right thing if its arguments happen to be arrays, so I use the following
simple if inefficient implementation:

static void deepEquals(Object x, Object y) {
     return Arrays.deepEquals(new Object[] {x}, new Object[] {y});

What that shows of course is that the messy logic you mention is already present in
Arrays.deepEquals so you could factor it out.

Éamonn McManus · JMX Spec Lead · http://weblogs.java.net/blog/emcmanus

Joseph D. Darcy wrote:
> Another piece of functionality requested in the j.u.Objects thread was a 
> deepEquals(Object a, Object b.) method that "did the right thing" if the 
> arguments happened to dynamically be arrays.
> I've been thinking a bit how this might be implemented.
> The array-ness of a and b would need to be determined, after any 
> up-front null-checks
> boolean aIsArray = a.getClass().isArray();
> boolean bIsArray = b.getClass().isArray();
> followed various case-analyses.
> if (aIsArray && bIsArray) {
>     Class<?> aComponentType = a.getClass().getComponentType();
>     Class<?> bComponentType = b.getClass().getComponentType();
>    if (aComponentType == bComponentType) {
>        // long case analysis to cast and call Arrays.deepEquals if 
> ComponentType is a reference type
>        // or the matching Arrays.equals(primitiveComponent[], 
> primitiveComponent[]) method if
>        // aComponentType.isPrimitive().
>    } else
>        return false;
> } else
>    return a.equals(b);
> Certainly a bit messy internally.
> What are scenarios where this method would be used?
> -Joe

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