Wednesday, April 22, 2009

set-by-index on a list, nCopies and STL vector(int)

javaList.set() means List.updateExisting().

If you construct an ArrayList with capacity of 999, and try to set value to position 888 you will fail.

You need to first populate 999 items into the array like this

new ArrayList<String>(Collections.nCopies(MAX_FIX_TAG, (String)null));

See http://docs.oracle.com/javase/tutorial/collections/implementations/convenience.html

STL vector ctor vector(int) does exactly the same. See http://www.cplusplus.com/reference/stl/vector/vector/

Q: If you construct a vector with a single argument 999, what's the size of the vector?
A: 0 in java, because 999 is interpreted as capacity, not array size.
A: 999 in STL. 999 default constructed elements inserted.

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