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#1
January 24th, 2013, 01:52 PM
 lisa92
Contributing User

Join Date: Oct 2011
Posts: 43
Time spent in forums: 10 h 33 m 29 sec
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ArrayIndexOutOfBounds error

This program takes as input an image, scans it and highlights circles in red. However I get an ArrayOutOfBounds exception at the last method when I call drawCircle(). I dont know how to fix it.

Code:
```public class Assig1 {

public static void main(String[] args) {
try {
// arg 0 is the input image name

// arg 1 is the min radius
int minr = Integer.parseInt(args[1]);
// arg 2 is the max radius
int maxr = Integer.parseInt(args[2]);

// if present, arg 3 is the max width we consider
int w = (args.length>3) ? Integer.parseInt(args[3]) : img.getWidth();
// if present, arg 4 is the max height we consider
int h = (args.length>4) ? Integer.parseInt(args[4]) : img.getHeight();

findCircle(minr,img, w, h);

//----
// write out the image
File outputfile = new File("outputimage1.png");
ImageIO.write(img, "png", outputfile);
} catch (Exception e) {
e.printStackTrace();
}
}

// Bresenham's algorithm to draw a circle
// requires circle center and radius, as well as the
// image and Graphics2D object with drawing colour already set.
static void drawCircle(int cx,int cy,int r,BufferedImage img,Graphics2D g) {
int f = 1-r;
int ddF_x = 1;
int ddF_y = -2 * r;
int x = 0;
int y = r;

// draw cardinal points
g.drawLine(cx,cy+r,cx,cy+r);
g.drawLine(cx,cy-r,cx,cy-r);
g.drawLine(cx+r,cy,cx+r,cy);
g.drawLine(cx-r,cy,cx-r,cy);

// draw 1/8 of the circle, taking advantage of symmetry
while(x < y) {
if(f >= 0) {
y--;
ddF_y += 2;
f += ddF_y;
}
x++;
ddF_x += 2;
f += ddF_x;

g.drawLine(cx+x,cy+y,cx+x,cy+y);
g.drawLine(cx-x,cy+y,cx-x,cy+y);
g.drawLine(cx+x,cy-y,cx+x,cy-y);
g.drawLine(cx-x,cy-y,cx-x,cy-y);
g.drawLine(cx+y,cy+x,cx+y,cy+x);
g.drawLine(cx-y,cy+x,cx-y,cy+x);
g.drawLine(cx+y,cy-x,cx+y,cy-x);
g.drawLine(cx-y,cy-x,cx-y,cy-x);
}

}

static void findCircle(int r,BufferedImage img, int w, int h) {

//getting all the pixels from an image
int[][] pixels = new int[w][h];

for( int i = 0; i < w; i++ ){
for( int j = 0; j < h; j++ ){
pixels[i][j] = img.getRGB( i, j );
}
}

// graphical output
Graphics2D g2 = img.createGraphics();
// use red
g2.setColor(Color.RED);

for (int i1=0; i1<pixels.length; i1++) {
for (int j1=0; j1<pixels[i1].length; j1++) {

if(pixels[i1][j1] != pixels[i1+r][j1]
|| pixels[i1][j1] != pixels[i1-r][j1]
|| pixels[i1][j1] != pixels[i1][j1+r]
|| pixels[i1][j1] != pixels[i1][j1-r]){
drawCircle(i1,j1,r,img,g2);
}
}

}
}
}```

#2
January 24th, 2013, 02:01 PM
 NormR
Contributing User

Join Date: Aug 2010
Location: SW Missouri
Posts: 3,582
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Quote:
 I get an ArrayOutOfBounds exception

Please copy the full text of the error message and post it here. It shows where the exception happened and the value of the index.

Remember array indexes range from 0 to the array length-1

#3
January 24th, 2013, 02:06 PM
 lisa92
Contributing User

Join Date: Oct 2011
Posts: 43
Time spent in forums: 10 h 33 m 29 sec
Reputation Power: 3
ArrayIndexOutOfBoundsException : -3
at Assig1.findCircle<Assig1.java:112>
at Assig1.main<Assig1.java:42>

#4
January 24th, 2013, 02:19 PM
 NormR
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Join Date: Aug 2010
Location: SW Missouri
Posts: 3,582
Time spent in forums: 2 Weeks 3 Days 2 h 49 m 10 sec
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Look at the values of all the indexes used on line 112 and see if any of them could be -3.

If you can not tell by looking, add a println statement that prints out the values of all the indexes used on that line to see which one has the value of -3.

#5
January 24th, 2013, 02:56 PM
 lisa92
Contributing User

Join Date: Oct 2011
Posts: 43
Time spent in forums: 10 h 33 m 29 sec
Reputation Power: 3
Updated

in the findCircle method I put i1 and j1 to start at r+1. (ie so that the image starts searching at after a given radius and not before that) but I still get same error this time instead of 3 it is 321

Code:
``` static void findCircle(int r,BufferedImage img, int w, int h) {

long timeBefore = System.currentTimeMillis();

//getting all the pixels from an image
int[][] pixels = new int[w][h];

for( int i = 0; i < w; i++ ){
for( int j = 0; j < h; j++ ){
pixels[i][j] = img.getRGB( i, j );
}
}

// graphical output
Graphics2D g2 = img.createGraphics();
// use red
g2.setColor(Color.RED);

for (int i1=r+1; i1<pixels.length; i1++) {
for (int j1=r+1; j1<pixels[i1].length; j1++) {

if(pixels[i1][j1] != pixels[i1+r][j1]
|| pixels[i1][j1] != pixels[i1-r][j1]
|| pixels[i1][j1] != pixels[i1][j1+r]
|| pixels[i1][j1] != pixels[i1][j1-r]){

//Question 3a). Measuring time
long timeAfter = System.currentTimeMillis();
long elapsed = timeAfter - timeBefore;
System.out.println("elapsed:" + elapsed);

drawCircle(i1,j1,r,img,g2);
}
}

}
}
}

```

#6
January 24th, 2013, 03:18 PM
 NormR
Contributing User

Join Date: Aug 2010
Location: SW Missouri
Posts: 3,582
Time spent in forums: 2 Weeks 3 Days 2 h 49 m 10 sec
Reputation Power: 347
Do you see what variable's content is causing the problem? When you fidn that, Then you need to check your algorithm to see why that variable has values outside the range of array indexes.

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