JAVA - Fixed length for loop giving ArrayIndexOutOfBoundsException

Question

Hey I don't know why but this loop is not working and giving me same error every time. If you know the fix please answer it down. And I am not able fix the issue.

Here is my loop

double angle = 0;

for (int i = 0; i < 120; i++, angle += 3) {
    int x = (int) Math.ceil(i * 8.5);
    int t = ((byte) (-Math.abs(bytes[x]) + 128))
            * (canvas.getHeight() / 4) / 128;

    points[i * 4] = (float) (getWidth() / 2
            + radius
            * Math.cos(Math.toRadians(angle)));

    points[i * 4 + 1] = (float) (getHeight() / 2
             + radius
             * Math.sin(Math.toRadians(angle)));

    points[i * 4 + 2] = (float) (getWidth() / 2
            + (radius + t)
            * Math.cos(Math.toRadians(angle)));

    points[i * 4 + 3] = (float) (getHeight() / 2
            + (radius + t)
            * Math.sin(Math.toRadians(angle)));
}

Here is my error

E/AndroidRuntime: FATAL EXCEPTION: main

Process: app.androidgrid.faysr, PID: 19297

java.lang.ArrayIndexOutOfBoundsException: length=128; index=128
     at app.androidgrid.faysr.visualizer.view.CircleBarVisualizer.onDraw(CircleBarVisualizer.java:94)
     at android.view.View.draw(View.java:17096)
     at android.view.View.updateDisplayListIfDirty(View.java:16078)

I also tried changing 120 to 128 and i < 120 to i <= 120 but it's not

Here is my java class

public class CircleBarVisualizer extends BaseVisualizer {
private float[] points;
private Paint circlePaint;
private int radius;

public CircleBarVisualizer(Context context) {
    super(context);
}

public CircleBarVisualizer(Context context,
                           @Nullable AttributeSet attrs) {
    super(context, attrs);
}

public CircleBarVisualizer(Context context,
                           @Nullable AttributeSet attrs,
                           int defStyleAttr) {
    super(context, attrs, defStyleAttr);
}

@Override
protected void init() {
    paint.setStyle(Paint.Style.STROKE);
    circlePaint = new Paint();
    radius = -1;
}

@Override
protected void onDraw(Canvas canvas) {
    if (radius == -1) {
        radius = getHeight() < getWidth() ? getHeight() : getWidth();
        radius = (int) (radius * 0.65 / 2);
        double circumference = 2 * Math.PI * radius;
        paint.setStrokeWidth((float) (circumference / 120));
        circlePaint.setStyle(Paint.Style.STROKE);
        circlePaint.setStrokeWidth(4);
    }
    circlePaint.setColor(color);
    canvas.drawCircle(getWidth() / 2, getHeight() / 2, radius, circlePaint);
    if (bytes != null) {
        if (points == null || points.length < bytes.length * 4) {
            points = new float[bytes.length * 4];
        }
        double angle = 0;

        try {
            for (int i = 0; i < 120; i++, angle += 3) {
                int x = (int) Math.ceil(i * 8.5);
                int t = ((byte) (-Math.abs(bytes[x]) + 128))
                        * (canvas.getHeight() / 4) / 128;

                points[i * 4] = (float) (getWidth() / 2
                        + radius
                        * Math.cos(Math.toRadians(angle)));

                points[i * 4 + 1] = (float) (getHeight() / 2
                        + radius
                        * Math.sin(Math.toRadians(angle)));

                points[i * 4 + 2] = (float) (getWidth() / 2
                        + (radius + t)
                        * Math.cos(Math.toRadians(angle)));

                points[i * 4 + 3] = (float) (getHeight() / 2
                        + (radius + t)
                        * Math.sin(Math.toRadians(angle)));
            }
        } catch (ArrayIndexOutOfBoundsException e) {
            e.printStackTrace();
        }

        canvas.drawLines(points, paint);
    }
    super.onDraw(canvas);
}}

I am also try-catch so, it won't crash the app, but the result is not as I am excepting.

The for loop iterates i from 0 to 119, but then the code uses multiples of i (`i * 4...`) to adress elements in the `points` array that is only 128 elements long (as the exception says). — david a., Jan 04 '18 at 12:58
You're accessing two arrays: `points[]` and `bytes[]`. The latter is indexed by `x` which is `ceil(i * 8.5)`. With `i == 15` the value of `x`will be 128 (`ceil(127.5)`) and also fits to your error message. Hence this could be a problem as well. — Ronald, Jan 04 '18 at 13:01
one of your arrays has a length of 128, so your max index is 127, since you're zero indexed. your loop appears to result in you trying to access an element larger than the array size. try commenting out each array element call and see which one is triggering the error. your `Math.ceil(i * 8.5)` call is going to hit 128 when `i=15` — mal, Jan 04 '18 at 13:04

score 1 · Answer 1 · answered Jan 04 '18 at 12:53

1

java.lang.ArrayIndexOutOfBoundsException: length=128; index=128 -> this means you are trying to access the 129th element of an array only containing 128 elements.

Remember, in Java arrays are 0 based, so the valid indices in your case vary from 0 to 127

answered Jan 04 '18 at 12:53

Stultuske

9,296
1
25
37

But the loop should be end at 120 – Ankit Suda Jan 04 '18 at 12:57
1

i ends at 120, but you use i * 4 and such as indices. when i is 100, that means you would try to get the 400 index. But you're not showing enough of your code for us to know for sure which line causes the problem – Stultuske Jan 04 '18 at 12:59
Ok wait I am updating the code. – Ankit Suda Jan 04 '18 at 13:00
assuming that CircleBarVisualizer is a class you made, check line 94, that's where it happens. – Stultuske Jan 04 '18 at 13:02
But the class ends at 89 :P – Ankit Suda Jan 04 '18 at 13:14
I updated the code – Ankit Suda Jan 04 '18 at 13:17
if it ends at 89, you are running a version compiled before you deleted lines. I didn't invent the '94' line, I copied it from the error method you posted – Stultuske Jan 04 '18 at 13:20
Yes, I removed some comments from the code. – Ankit Suda Jan 04 '18 at 13:21
so, compile and run it again, and check the (new) error message what line to check – Stultuske Jan 04 '18 at 13:22
Same error but this time it says line no. 61 which is int x = (int) Math.ceil(i * 8.5); – Ankit Suda Jan 04 '18 at 13:24
that line can not possible throw an ArrayIndexOutOfBoundsException, because there is no array involved there. – Stultuske Jan 04 '18 at 13:28

score 1 · Accepted Answer · answered Jan 04 '18 at 13:01

For i = 0 ... 120, on the final iteration of your loop the following statement:

points[i * 4 + 3]

would be trying to access the 479th element of an array ((119 * 4) + 3 = 479) that only contains 128 elements.

In order to fill your array, you want i < 31 because (31 * 4) + 3 = 127.

score 0 · Answer 3 · answered Jan 04 '18 at 13:03

Even you have for loop, which iterate for index 0 to 120, but inside your for loop you are trying to access different index (i * 4, i * 4 + etc), which is causing actual issue.

Imagine, you have points array of 2 size. Now, on first iteration, i would be 0, but you would be trying to access element i * 4 + 3, which would be equivalent to 3. But, points array size is 2.

Since, you are trying to access element i * 4 + 3 (which would be higher end in each iteration). I would suggest to change your for loop to something to avoid ArrayIndexOutOfBoundsException (if array size is 120)

 for (int i = 0; (i * 4 + 3) < 120; i++, angle += 3) {

Christophe Tela · Answer 4 · 2018-01-04T15:44:23.207

-1

You must review the size of the "points" array. Considering your code, its size should be at least (119 * 4 +3), i.e. 479.

"points" array size is 4 * "bytes" array size, but your code doesn't show what is the "bytes" array size; probably something defined in the ancestor class.

edited Jan 04 '18 at 15:44

answered Jan 04 '18 at 12:57

Christophe Tela

11
2

JAVA - Fixed length for loop giving ArrayIndexOutOfBoundsException

4 Answers4