A List of Names — Collecting Values

Student: Professor, I’m unsatisfied with what we’ve learned. I feel like you’re not telling the whole story.

Prof: Oh? In what way?

Student: Well, we talk about records for storing students, but not a whole list of them. Surely things like TSS don’t have a different definition for every student. And there was an example with a ShoppingItem or something like that, but it only had one item in it. When you shop online your cart is a whole bunch of different items. And a lot of pictures you might want to make have lots of little pieces, like a lot of stripes or something like that. I don’t see at all how you’d do that with what you’ve shown me.

Prof: Ah, you want to create collections or sequences of values of the same type!

Student: Uh, yeah? Sure, I guess, that sounds kind of right.

Prof: There are a lot of ways to do that in Java, but arrays are one really common tool. Here’s an array in Java, and how to access its pieces:

String[] names = { "Anya", "Rachel", "Neelkanth", "Sydney", "Daniela", "Gonzalo" };
String anya = names[0];
String rachel = names[1];
String sydney = names[3];
int gonzaloIndex = 5;
String gonzalo = names[gonzaloIndex];
int numberOfNames = names.length;

Student: OK, so the array itself is stored in names, and you can use the [] to look it up? And indexes start at 0?

Prof: That’s right. We call array[i] array indexing, and i has to be an int that is between 0 and the size of the array minus 1

Student: Why minus 1?

Prof: Well, how many elements are in that array (we call each value in an array an element)?

Student: Six…

Prof: And what’s the index of the last one?

Student: You made a definition for it, it was 5… oh! I see.

Practice

Here is an array of doubles:

double[] temps = { 72.5, 68.0, 75.2, 80.1 };

Which of these are valid ways to index temps? Select all that apply.

temps[0]
temps[3]
temps[4]
temps has 4 elements, so the last index is 3.
temps[-1]
Indexes start at 0; there is nothing before it.
temps[1.0]
An index has to be an int, even when the elements are doubles.