JavaCard OS

I need to create about 300 byte arrays ( new byte {... } ) in my applet. But somebody told me that I should not create that much arrays since there will be overhead of about 4 bytes, associated with per array. Can anybody help me confirm this? thanks

There indeed would be an overhead for the array itself.

And this overhead information may be only known by the javacard OS manufacturer, I suspect.

I have seen some platforms that have a 7 bytes overhead for objects.

It's not specified. It really depends on the platform.