Why do dynamic arrays in C ++ and Java have different initial capabilities?

Question

So, I was looking for how a dynamic array works in general. I found two different concepts.

In c ++

In C ++, a dynamic array is usually implemented by vectors. Vectors set the capacitance to 0, increment the counter to insert a new element, and then double the size of the capacitance for new inserts.

vector.h

/*
 * Implementation notes: Vector constructor and destructor
 * -------------------------------------------------------
 * The constructor allocates storage for the dynamic array and initializes
 * the other fields of the object.  The destructor frees the memory used
 * for the array.
 */

template <typename ValueType>
Vector<ValueType>::Vector() {
   count = capacity = 0;
   elements = NULL;
}

To expand the size of the vector

/*
 * Implementation notes: expandCapacity
 * ------------------------------------
 * This function doubles the array capacity, copies the old elements into
 * the new array, and then frees the old one.
 */

template <typename ValueType>
void Vector<ValueType>::expandCapacity() {
   capacity = max(1, capacity * 2);
   ValueType *array = new ValueType[capacity];
   for (int i = 0; i < count; i++) {
      array[i] = elements[i];
   }
   if (elements != NULL) delete[] elements;
   elements = array;
}

In java

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Answer 1

, std::vector ( , ). , ~ 10 , std::vector::reserve:

std::vector<int> vec;
vec.reserve(10);

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Answer 2

0?

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Answer 3

I used an implementation that stores the default value of 32 elements per vector. It was an embedded implementation of Sun C ++ STL. It was a disaster. I had a perfectly reasonable program, which by its nature should have had about a hundred thousand of these vectors. He did not have enough memory. And it should have been perfect, because of those hundreds of thousands of elements, only a small percentage had these vectors not empty.

So, from personal experience, 0 is the best default vector size.