Basic dynamic array question. Use of new versus no new.

[WhatMeWorry via Digitalmars-d-learn]

In Mr. Cehreli's book it says

Additionally, the length of dynamic arrays can be changed by 
assigning a value to this property:

int[] array; // initially empty
array.length = 5; // now has 5 elements

while in Mr. Alexandrescu's book, it says

To create a dynamic array, use a new expression (§ 2.3.6.1 on 
page 51) as follows:

int[] array = new int[20]; // Create an array of 20 integers


Could someone please compare and contrast the two syntaxes. I 
presume the "new" command places the 2nd array in heap memory.