Object.isArray() is slow, is there a fast way to do that?

Question

In my application obj.getClass().isArray() is called very frequently and become the bottleneck of the app.
I want to check efficiently at run-time if an object is an array. Primitive array and object array should return true.
The way I can imagine is to instanceof all primtive arrays, but cannot handle types like int[][]. And the app is used as lib, so I cannot list all types.
Is there any clue for that?

Answer 1

A benchmark I've just done gave the following results:

{s instanceof Object[]} spends 44ms
{s.getClass().getName().charAt(0) == '['} spends 58ms
{s.getClass().isArray()} spends 303ms

Benchmark has been done using Benchmark.java, called with Main.java.

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After having discussed the use of a final variable in the above benchmark, see the new results using a local one:

{s instanceof Object[]} spends 83ms
{s.getClass().getName().charAt(0) == '['} spends 93ms
{s.getClass().isArray()} spends 354ms

Even if the durations are all a bit longer (interesting btw), their order has been preserved.

Benchmark.java has been then called with this new Main.java.

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And using a primitive array called with this other Main.java:

{a instanceof int[]} spends 71ms
{a.getClass().getName().charAt(0) == '['} spends 82ms
{a.getClass().isArray()} spends 340ms

Still the same results order.