数组索引超出范围异常 [英] Array index out of bounds exception
问题描述
当我运行这个应该检测图像中的圆圈的程序时，当我调用drawCircles（）
When I run this program that is supposed to detect circles in an image I get Array index out of bounds exception at the last method when I call drawCircles()
时，我在最后一个方法得到数组索引超出范围的异常findCircle（）读取图像并搜索圆圈，drawCircles（）使用Bresenaham算法绘制它们。
findCircle() read the image and searches for circles and drawCircles() draws them using Bresenaham algorithm.
public class Assig1 {
public static void main(String[] args) {
try {
// arg 0 is the input image name
BufferedImage img = ImageIO.read(new File(args[0]));
// 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();
// you can look at pixel values with this API call:
int c = img.getRGB(0,0); // get RGB value of pixel at (0,0)
// you can write out pixels with the setRGB() API. However,
// what you get will depend on the colour model, so here
// we use a Graphics2D object.
// graphical output
Graphics2D g2 = img.createGraphics();
// use red
g2.setColor(Color.RED);
// call circle drawing algorithm
drawCircle(5,5,3,img,g2);
//-----
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);
}
}
}
}
}
推荐答案
在你的findCircle方法中，
In your findCircle method,
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);
}
如果r不是0，这将导致数组索引超出范围异常因为你基本上是从第0个索引循环到第n个索引。基本上你在增加或减去r的任何地方。例如，这是导致此错误的一个语句
If r is anything but 0 this will cause an array index out of bounds exception since you're basically looping from the 0th to the nth index. Basically anywhere you're adding or subtracting r. For example, this is one of the statements that will cause this error
pixels[i1+r][j1]
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