Question

Or is there any way to cast a generic object(that originally was a 2Darray) to a 2d Array without knowing its size?

I have a program where the user enter data and that data is submitted into a 2D array that varies in size depending on how much the user entered. I saved the array as an object to file using what I learned from this tutorial.

http://beginwithjava.blogspot.com/2011/04/java-file-save-and-file-load-objects.html

([to save] open file, open object stream, write objects, close)
([to restore] Open a file. Open an object stream from the file. Read objects to stream.
Cast objects, Close the stream and file.)

However, since I can’t know how large the 2d array will be, I can’t figure out how to cast the object back into a 2dArray when it comes time to restore.

Answer 1

There is no way to know the size ahead of reading, so the most common solution is to save the size before saving the data. The reader than reads the size, allocates enough memory, and procedes with reading the data the regular way.

The other less common way is to save markers in the file to indicate where each row of data ends. In a way, this is similar to null-terminating your strings in C, where the length of the string is not stored explicitly, but must be recomputed each time. This method has a disadvantage of not allowing pre-allocation. In other words, you would either need to allocate enough memory to accommodate the data of any legal size, or re-allocate dynamically as you go.