★ array creation and access

• most programming languages have a simple data structure for a collection of related data.
  • block-based programming: called a list
  • others (like java): array
• array — block of memory that stores a collection of data items (elements) of the same type under one name.
  • useful when you have many elements of data of the same type you want to keep track of, but you don’t need to name each one
  • you use the array name and a number (index) for the position of an item in the array
  • you can make arrays of ints, doubles, Strings, and even classes that you have written
  • (it’s like a row of small lockers, but you can only store value each locker)
• most languages start from the number 0 when counting elements
• when we declare a variable, we specify its types and then the variable name. if we want to make a variable into an array, we put square brackets after the data type
  • for example, int[] scores means we have an array called scores that contains int values
  • the declarations do NOT create the array. arrays are objects so any variable that declares an array holds a reference to an object
  • if the array hasn’t been created yet and you try to print the value of the variable, it will print null
• two ways to create an array:
  • keyword new to get new memory
  • use an initializer list to set up the values in the array
• use the new keyword with the type and size of the array (the number of elements it can hold) - which will create the array in memory
  • declaration & creation in one step

//declare an array variable
int[] highScores;
// create the array
highScores = new int[5];
// declare and create array in 1 step!
String[] names = new String[5];

which of the following creates an array of 10 doubles called prices?

A) int[] prices = new int[10];

B) double[] prices = new double[10];

C) double[] prices;

D) double[10] prices = new double[];

• answer

<aside> 🧾 note: array elements are initialized to default values

• 0 for elements of type int

• 0.0 for elements of type double

• false for elements of type boolean

• null for elements of type String </aside>

• when using an initializer list, you set the values in the array to a list of values in curly braces when you create it

  • you don’t specify the size, it will determined from the number of values that you specify