How many parameters does the varargs facility permit in java?

Question

I am interested in knowing how many parameters you can pass using the varargs facility in Java.

Is there a JVM or Memory limit? As far as I can understand it varargs is implemented as an array so the limit is determined by the amount of memory. Is this correct?

Answer 1

Varargs is syntactic sugar for an on-the-fly array that is just large enough to fit the elements coded.

The limit then would be the size of an array, which is 2 ³¹ (ie large).

Considering the size is specified by the actual number of parameters coded, you will never have to worry about it.

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A quick test confirms that the usual method parameter count of 255 does not apply to individual varargs elements.

Answer 2

Yes there is. Try to allocate the memory which is greater than your Pergemn memory, that throws OutOfMemory .

note that there is no speciality about array or varargs here. You can freely use your memory below the memory you allocated.

I hope this is just for learning and not using those many in your application.

Answer 3

There is no explicit limit for the number of variable arity arguments. However the method size is limited. It should not exceed 65535 bytecodes .

When javac compiles a call to a variable arity method, it creates and fills the array using the pattern like:

+0: dup
+1: bipush <index> (or sipush if index > 127)
+3: iconst_0
+4: iastore
+5: dup
    ...

So, filling one array element takes 5 or 6 bytecodes.
This means you can practically call a method with a little more than 10K arguments .