When is a generic array absolutely necessary -- a case

Question

This Q is to look for a sample case where a generic array is absolutely necessary.

Generics and arrays "don't mix well".

Is there a case where a generic ArrayList won't do-- a generic array has no substitute and has to be used.

Effective Java leaves a door open for generic arrays saying that there may be cases where a generic array is necessary.

I've been using ArrayList without any shortcomings and can't think of a case like this.

TIA.

Note: i've seen these:

• How to create a generic array in Java?
• Generic List and Generic Array
• Generic array creation error
• Java generics and Array's

Along with some other discussions.

Answer 1

Some points:

• If you have some "legacy" library then you're bound to the types that they use. This could be arrays.

• If you handle native code then arrays will be a more natural way to exchange data with the native code.

• If you access binary data (e.g. sound files or similar) then using an array can help.

• If you handle big amount of binary data then an array could be more efficient.

So there are many reasons why an array could be helpful (especially with primitive types).

If you only handle objects then it is most times easier to use a List.

Answer 2

I would say that Bloch meant convenient instead of necessary, arrays are simpler structures, easier to handle.

As a data structure, from a functionalities point of view, ArrayList are interchangeable with array.

Arrays are obviously more lean memory-wise but require additional effort to get some basic functionalities (i.e. manual array resizing when the original array is not big enough to hold a new element) but other functions are already provided by the runtime (Arrays class).

ArrayLists are backed by actual Object arrays so there isn't much difference performance wise, for common operations like searching and sorting (when using the same algorithm).