Processing language: Get inner array values from ArrayList()

Question

I'm trying to use the ArrayList() method in Processing.

I have this:

    ArrayList trackPoints = new ArrayList();

        //inside a loop
        int[] singlePoint = new int[3];

        singlePoint[0] = 5239;
        singlePoint[1] = 42314;
        singlePoint[2] = 1343;
        //inside a loop

    trackPoints.add(singlePoint);

So basically I want to add an array "singlePoint" with three values to my ArrayList.

This seems to work fine, because now I can use println(trackPoints.get(5)); and I get this:

[0] = 5239;
[1] = 42314;
[2] = 1343;

However how can I get a single value of this array?

println(trackPoints.get(5)[0]); doesn't work.

I get the following error: "The type of the expression must be an array type but it resolved to Object"

Any idea what I'm doing wrong? How can I get single values from this arrayList with multiple arrays in it?

Thank you for your help!

JB Nizet · Accepted Answer · 2011-10-10 16:07:35Z

6

Your ArrayList should by typed :

List<int[]> list = new ArrayList<int[]>();

If it's not, then you're using a raw List, which can contain anything. Its get method thus returns Object (which is the root class of all the Java objects), and you must use a cast:

int[] point = (int[]) trackPoints.get(5);
println(point[0]);

You should read about generics, and read the api doc of ArrayList.

answered Oct 10, 2011 at 16:07

JB Nizet

694k94 gold badges1.3k silver badges1.3k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Ted Hopp Over a year ago

The last can be abbreviated println(((int[]) trackPoints.get(5))[0]);. It saves a line and a temp variable, but the two-line version is a bit easier to read.

John Kugelman · Accepted Answer · 2011-10-10 16:16:35Z

0

The get() method on ArrayList class returns an Object, unless you use it with generics. So basically when you say trackPoints.get(5), what it returns is an Object.

It's same as,

Object obj = list.get(5);

So you can't call obj[0].

To do that, you need to type case it first, like this:

( (int[]) trackPoints.get(5) )[0]

edited Oct 10, 2011 at 16:16

John Kugelman

364k70 gold badges555 silver badges600 bronze badges

answered Oct 10, 2011 at 16:08

Yohan Liyanage

7,0204 gold badges48 silver badges65 bronze badges

Collectives™ on Stack Overflow

Processing language: Get inner array values from ArrayList()

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related