Re: ClassCastException on Array content cast

From:

Tom Anderson <twic@urchin.earth.li>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 7 Aug 2009 00:17:11 +0100

Message-ID:

<alpine.DEB.1.10.0908070015240.18644@urchin.earth.li>

On Thu, 6 Aug 2009, Bill McCleary wrote:

Lew wrote:

RVic wrote:

Answered my own q [sic] -- in case anyone hits this in the future on a
search, should be:

Given that the two forms of toArray() are document right adjacent to each
other in the Javadocs, it shouldn't be hard to find one given the other.

arrayList.toArray(dmFieldInfos); //provided dmFieldInfos is th correct
length

dmFieldInfos can be any length. It is common to see this idiom as:

DmFieldInfo [] dmFieldInfos = arrayList.toArray( new DmFieldInfo [0] );

How cheap is the creation and discarding of the zero-length array here?
My guess would be decently cheap with a modern

The birth and death of the size-zero array will be cheap. The reflection
needed to determine its element type and create a matching right-sized
array might not be. I tend to spend the extra characters on creating a
correctly-sized array here just in case.

GC and especially if, after using it for type inference, the compiler
sees that it's never used and optimizes it away.

If the compiler can do that, then yes, the cost will be negligible. That
strikes me as a pretty impressive thing to do, though.

(If not javac, the JIT.)

Definitely not javac.

tom

--
The sunlights differ, but there is only one darkness. -- Ursula K. LeGuin,
'The Dispossessed'