Question

Which way is better for initializing a Java List:

• new ArrayList<String>(futureSize)

• new ArrayList<String>(futureSize + 1)

(in order to prevent resizing of the list)

futureSize is the future size of the list once filled.

Note : If you are going to comment/answer anything about “premature optimizaton is…”, “you should instead…”, PLEASE DON’T. I am looking for an answer to my question, that’s all.

Answer 1

You can see from the implementation of add(E e) and (similar methods)

public boolean add(E e) {
    ensureCapacity(size + 1);
    elementData[size++] = e;
    return true;
}

… that you should not run into trouble (i.e. the internal array is not resized) if you use

new ArrayList<String>(futureSize)